I'm afraid mate it is probably April in isolation - we win 3 of 4 that month... then lose 3 of 4 in May!
Looking back...
March:
We lost to Stoke and Arsenal away.
Then Barry got injured/suspended and we started playing in a 4-4-2/4-1-4-1, with McCarthy at the heart of it.
We then beat Newcastle, QPR and then I think Southampton. Drew at Swansea, beat Burnley, hammered United and then drew or lost to a side we really should have hammered.
I remember at the time though McCarthy really stepped up to the plate in that run, which lifted us from 14th/15th up into 11th and away from any danger.
At his best, he makes us tick. At his worst, he still gets about and makes good tackles and interceptions but lacks some guile in possession that Besic has.
However, he's key to us playing well so gets my vote every time for now unless he really is in poor form. As it is, since returning from injury he's had two very good games, one average game and two (by his standards) sloppy ones but nothing majorly bad on the whole.
No need to rush Besic back and have him get injured straight away again. Fact does remain when McCarthy is in the team we win more games than when he isn't, no matter how he plays.