I did pretty well with a 4-3-3 with Man Utd. Initially I was using a DM rather than an AMC, and heavily relying on the AML/AMR and DL/DR Wing Backs for the attacking play with my ST either as a DLF or a P - with a Control/Balanced formation. I switched things up at the end of the 1st Season as...
Yohan Cabaye has been a good investment on my side. He's a strong midfielder. I'd rate him at least better than Carrick in my line-up, and with Sandro - they're an excellent team.
Lars Bender is a very good DM, especially if you put him on the field with Carrick & Fletcher. Have him as your AM, and he's brilliant. He can also play CM, and is good at being an allround CM. He's a hard purchase to snaffle though, so you'll have to work hard.