[Brightcolours]

If you shoot mostly portrait, FF makes more sense IMO.

 

Now, if AF accuracy for is your main concern, you should consider mirrorless instead. AF accuracy is much more reliable and accurate than any DSLR. If portrait is what you're after, you should strongly consider Fuji (the 56 f1.2 and 90 f2 are fantastic portrait lenses).

Your AF ideas about DSLRs live in the past still... The 5D mk III is very capable of focussing accurately with very shallow DOF. And fast at that.

 

Toni-a, I forgot which lenses you have. Of course, lenses play a big part in the result. For portrait, FF makes more sense unless you never use shallow DOF in portraits.