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).
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).