A Team:
GK: Buffon (Juventus, Italy)
DL: Chiellini (Juventus, Italy)
DR: Alves (Sevilla, Spain)
DC: Toure (Arsenal, Ivory Coast)
DC: Barzagli (Palermo, Italy)
ML: Silva (Valencia, Spain)
MR: Messi (Barcelona, Argentina) OR Ronaldo (Man Utd, Portugal)
MC: Fabregas (Arsenal, Spain)
MC: Kaka (AC Milan, Brazil) OR Mascherano (Liverpool, Argentina)
FC: Fred (Lyon, Brazil)
FC: Aguero (At. Madrid, Argentina)
Team speaks for itself really. All of them are amazing players. There's nobody in the game who can control the midfield like Fabregas can. Not Kaka, not Iniesta, not Gerrard - nobody. I've given another option with Kaka just in case you fancy playing a DM and Mascherano is the best. Messi and Ronaldo are on the par on the right wing. Both just as good so no point choosing. Silva OWNS the left wing. Aguero everyone knows about. Fred is just incredible. He's got everything a striker needs. Just incredible. Toure and Barzagli easily the 2 best defenders in the game. Terry is very close competition but Toure shades it over him because of his pace. Chiellini and Alves are the two best full backs. No doubts about that either. Buffon is much better than Cech, Casillas, Ustari, Akinfeev or anyone else. Awesome GK.
B Team
GK: Cech (Chelsea, Czech Republic)
DL: Clichy (Arsenal, France)
DR: Sagna (Arsenal, France)
DC: Terry (Chelsea, England)
DC: Nesta (AC Milan, Italy)
ML: Rosicky (Arsenal, Czech Republic)
MR: Van Persie (Arsenal, Holland)
MC: Iniesta (Barcelona, Spain) OR Veloso (Sporting CP, Portugal)
MC: Gerrard (Liverpool, England)
FC: Henry (Barcelona, France)
FC: Ibrahimovic (Inter, Sweden)
I wasnt sure if by "B team" you meant a second choice team or team of youngsters. That's a second choice team. Not much to say really. I know the ML and MR positions have 2 questionable players, but they've both been amazing for me on those wings. And they can switch flanks so easily as well. Henry is still a God regardless of his age. Sagna is a RB that HAS to tried to be believed. Incredible.
Youngsters (21 and under at the start):
GK: Ustari (Getafe, Argentina)
DL: Traore (Arsenal, France)
DR: Behrami (Lazio, Switzerland)
DC: Djourou (Arsenal, Switzerland)
DC: Criscito (Juventus, Italy)
ML: Guardado (Deportivo, Mexico)
MR: Walcott (Arsenal, England)
MC: Denilson (Arsenal, Brazil) OR Lucas (Liverpool, Brazil)
MC: Nasri (Marseille, France) OR Lulinha (Corinthians, Brazil)
FC: Vela (Arsenal, Mexico) OR Saivet (Bordeaux, France)
FC: Bojan (Barcelona, Spain)
Again, pretty straight forward. Denilson is better than Lucas
imo but thats a bit of bias as well (Arsenal fan!). Bojan is THE best young ST. Vela, Saivet, Pato are all pretty much equal. I've got experience with Vela and Saivet so I put them in. Nasri is an awesome AMC. As is Lulinha. I suppose you could find someone better for MR but I love Walcott's pace and he's always a great supersub for me. Most of the times when he's on, he provides atleast one or two crosses to score from.