Montreal, but i'd like to see both playing on the left side, if we need to be more defensive. Both of them can play as LMs.
I wouldn't classify anyone as having a "great season" for us. Wilshere and Cazorla have been our best players but i wouldn't put them in the "great season" category. Gibbs has had a fair few iffy moments for me.
Gibbs started the season well but was poor for about 6 weeks leading up to his injury. Monreal has been decent apart from the Spurs game, but too soon to judge. Monreal deserves more chances.
Gibbs seems to have a good connection with Podolski and when those two are playing together on that left hand side, we seem to create a lot from that side. I would bring back Gibbs for that, our defence is a mess anyway, might as well bring back Gibbs and so he can gives more pace going forward.
As an outsider, I'd have to suggest giving Monreal a run and seeing what he can do. He seems to have all of the qualities required for a balanced full-back and doesn't have Gibbs' fitness issues, but there's clearly a communication problem between your defenders. He's new to the country and has joined in the middle of the season, so there's bound to be some teething problems.
Monreal is a better defensively, Gibbs is better offensively, so play Monreal against the fast pacy teams and Gibbs against the 11 men behind the ball teams.
Theo IMO. He doesn't track back and when he does he offers little defensively. I'd play Oxo seeing as how Theo is out of form ATM
The OX has been pretty terrible in his last few games to be fair. If we are going drop Walcott, then I would move Cazorla to the right and play Rosicky in that role behind the CF.