My pick: always only Messi.
Without Xavi, Iniesta, Busi, we would probably have Thiago, Cesc and we would buy 2-3 players like Rakitic or Kroos.
Messi would win CLs with them also.
On the other hand, if you put Xavi-Iniesta-Busi and ANY other attacking trio, CL is not that certain anymore.
Especially if you have to face another team who has Messi.
Just imagine:
-- would you play against Real Madrid team in a CL final which has the same team as today + Xavi-Iniesta-Busi (at their prime) in their midfield against us?
-- or would you play against the current Real Madrid, with already good midfield and attack, plus they would have Messi (in his prime) in attack?
I don't want to play against Messi. Ever.
You can't win against Messi on larger samples.
Messi is an overpowered "cheater".