OK. I thought it might be a fun exercise to compare notes on who and how you would line up your team for their 1st match of the season. I guarantee that there will be such variety even for the same teams. Here are a few simple Guidelines:
RULE #1 - You may ONLY pick players that are currently on your roster and are not injured (or if injured expected to be fit within the next few days). In other words, if you are a RM fan you may not include Modric, and so on....
RULE #2 - If you would choose the exact same line-up as a previous poster simply say "I agree with so and so" to avoid redundancy
SUGGESTION #1 - The team can be your ideal 1st 11 for the season or one that
it more catered to your opponent on opening match day. For example, if
you are playing against Stoke City you may want to choose a Defensive
midfielder that you wouldn't otherwise include. You get the idea

SUGGESTION #2 - If you pick a player or formation that is non-conventional it
would be best if you summarize your reason in a quick line
SUGGESTION #3 - I would like to see as much of a variety of teams as is possible so try to get involved. I would like to avoid an entire thread of only Arsenal, Manchester United & Barcelona line-ups. Lastly, if you think you have a good suggestion for a team besides the one you follow feel free to add that as well.
Let's see what you got!

I shall begin.

MY CURRENT ARSENAL 11:

Formation - 4231

GK- Szczesny
LB - Gibbs (more defensively sound than Santos)
CBs - Vermaelen & Mertesacker (Don't think Koscielny will be fit in time)
RB - Coquelin (Sanga is obviously injured + I think he's more defensively sound than Jenkinson + Yenarris is too young to start on the 1st match of the season)
CDM - Song
Deep-Lying Playmaker - Arteta
AMF - Cazorla
LW - Gervinho (on red hot form + Podolski is not 100% match fit)
RW - Theo Walcott
CF - Giroud

I will go on with Liverpool: 4-3-3

                Pepe Reina
Johnson - Skrtel - Agger - Enrique
 Gerrard - Lucas Leiva - Joe Allen
     Downing - Borini - Suarez

@Ihaveabbc, what do you think of Shelvey? He's got huge potential IMO

Manchester United 4-2-3-1
GK: De Gea - After having about 13 clean sheets last season, I hope that he can blossom into a world-class goalkeeper. He was fantastic last season making amazing saves.
RB: Rafael - Seeing him in the Olympics was a joy. Barely let anyone past him. Has a lot of potential, this boy.
CB: Vidic - Return of the King! I'm not sure if he'll be fit enough to play the full 90 minutes but we have to let him get the groove of things after being out of such a long time.
CB: Ferdinand - He was O.K. last season. His best days aren't behind him but I hope he still performs this season.
LB: Evra- Performance was disappointing last season but played well in the pre-season. Again. Just like Ferdinand. His best days aren't behind him but I hope he plays good in the new season.
DM: Carrick - Played as a centre-back in the Hannover match. Played O.K. but I think that a mix of defense and midfield would be great for Carrick.
DM: Anderson - Anderson was one of the players that could have been AMAZING. He didn't do so well for the past few seasons but dear oh dear. He was amazing in the pre-season worthy of putting on the 11 XI. Has an amazing left-foot.
RW: Nani - He was amazing against Barcelona and the pre-season. Barely let the ball get away from him tricking the opponents with his blistering feet. Just don't dive and improve in penalties. :)
CAM: Kagawa - Made me understand why SAF bought him. Top quality and played amazing in the pre-season. Hope to see him do well on his debut in the Premier League
LW: Valencia/Young - Valencia was a little disappointing in the pre-season. Seemed to have a lot of pressure having Number 7. Young was not that great either but wasn't horrible. Hope he finds his feet and performs.
ST: Rooney: Played well against Hannover and in the pre-season as well. Scored an AMAZING free-kick.
Just hope he gets more consistent with penalties and doesn't miss open goals. XD.

Let's get that 20th title and bring the trophy back to Old Trafford.
GGMU

          Barcelona 3-4-3:

                 Valdés

   Piqué - Mascherano - Jordi Alba

Dani Alves - Xavi - Fàbregas - Iniesta

       Sánchez - Messi - Afellay

Subs: Puyol, Busquets, Villa

man united 4-4-2
GK-Lindegaard (good form for pre-season, stronger than de gea & against everton-physical side)
RB-Jones (rafael could be unfit from olympics...everton are physical so jones would be more suited)
CB's-Vidic, Ferdinand
LB-Evra

RM-Valencia
CDM-Carrick
CAM-Kagawa
LM-Young (just improve on penalties!!!! and i think he would be more suited against everton than nani...)

ST-Rooney
ST-Welbeck

i like the look of man_utd's line up, even better than mine haha. but this would be a decent alternative i think.

@thijsFCB: Those are some interesting choices you got there. Care to explain why you would start Affellay over Villa? Also don't you think if you play a 3-4-3 a lack of a DM would be suicide?

@manutd: "Rafael - Seeing him in the Olympics was a joy." yea he was a joy to watch for me (but that's bc I wanted Mexico to win). "Barely let anyone past him." Seriously, dude did you see his last match? sorry man - had to say it :b
Also, surprised you'd pick Anderson over Cleverly who I think has been fantastic.

Spurs - 4-4-1-1

GK: Friedel
RB: Walker
CB: Vertonghen & Kaboul
LB: Assou Ekotto
RM: Lennon
CM: Huddlestone & Sigurdsson
LM: Bale
CAM: VDV
ST: Defoe

@Jim: that back line looks pretty solid I must say. BTW, when will Parker be back?

I still think we need a new LB, Ekotto can be good at times but can also be highly unreliable...They said they thought about a month after his surgery, so should be early September if things go well.

@Jim: sorry, forgot to ask you my main question - why would you start Kaboul over Dawson? Is he still crocked?

Dawson looked very shaky at the back last season when he was fit which all be it wasn't for very long and has no pace at all, and Kaboul is rock solid at the back the majority of the time and rarely makes mistakes.

@heisinburg: yes, he certainly has but i am pretty conscious that BR wants to Play Joe Allen in the starting line-up and maybe he will use Shelvey in the Second half as a Substitute. 

@ Footaholic
I agree. Rafael was horrible in the last match. The Brazil FA also said it was his fault for the loss.
But in the other matches, he was actually great. And if I need an alternative, Jones and Smalling is on the bench but I still think Rafael is a top player. He's only 22.
However to me. Anderson was awesome in the pre-season. That's just a matter of choice.
Cleverley didn't do too well against Korea and other teams in the Olympics.
Nonetheless. That's meh squad.

Manchester United: 4-4-2
GK: Lindegaard
RB: Valencia
CB: Ferdinand & Vidic
VB: Evra
LW: Young
CM: Cleverly
CM: Kagawa
RW: Nani
ST: Rooney & Welbeck

I picked Lindegaard rather than de Gea simply because I think he's a steadier goalie than De Gea at the moment. Incredible saves aren't everything.

Valencia is only improving more as a right back. He has got some great runs, and is in general good defensively. Adept at using his speed.

It's surprisingly few who chooses Cleverly now that he's 100% ready. A better card than Anderson, Carrick and Scholes in my opinion.

I agree with @Golden regarding Manchester United.

Also, allow me to set up my personal choice regarding Real Madrid's strongest team at the moment: 4-2-3-1

GK: Casillas
RB: Ramos
CB: Carvalho & Pepe
LB: Coentrão
CDM: Alonso & Khedira
LW: Ronaldo
CAM: Özil
RW: Di María
ST: Benzema

I know, the defensive line will be criticized. But honestly, this is the safest and most balanced way to set up our defense. Now, as I'm a Madridista, I know that in an 'El Clásico', Mourinho picks a non-injured Carvalho before Arbeloa. In addition, Carvalho seems to have shaked off his injury when the upcoming season will start. Anyway, by using Carvalho, Ramos is pulled out to the RB (where he ordinary played until Carvalho got injured), while Pepe and Carvalho covers the CB's.

Furthermore, with reference to the left back, I think Coentrão has reached Marcelo. I'm pretty sure I share this thought with lots of other Real supporters, despite Marcelo's loyalty to our club. He was the more reliable one last season as Coentrão came from Benfica one year ago, but now it's going to be opposite. However, they're amazingly equal while running down the flank (I mean it, I seriously can't tell who's the best offensively), but Coentrão is capable of running more and he does a better effort defensively. It's truely like his stamina is never ending or something.

Özil in front of Kaká would be the most natural choice these days. Benzema looks fresher and more hungry than Higuaín here and now, but that can change. They're a bit like Coentrão and Marcelo.

I apologize my long post, I just had to explain my defensive choice in depth. On the other hand, what I'm sure of is that it would've been a lot of questions around the defensive blah blah.

Our injury situation is bad but:

J. Perreira -- V. Ruiz -- A. Rami -- J. Mathieu

              
                 F. Gago -- T. Costa

   S. Feghouli --  G. Jonas -- A. Guardado

 
                      R. Soldado

we play 3-5-2

Handanovic

Maicon -- Lucio -- Nagatomo

Cambiasso -- Zanetti

Coutinho -- Sneijder -- Guarin

Pazzini/Alvarez --- Milito

@Ronaldo-R9: I'm fairly certain Lucio was traded to Juve.