I think it all dives down to what one wants. I'm used to drifting RWD, and given the short time (1 week) I was allowed to play GT4 a few weeks back, I didn't get to do too much actuall drifting. Just concentraiting on grip driving.
For what time I have been able to drft, I've found I'm best drifting with FR (such as the Ginetta G4...I'm sure I miss-spelled that, also the Corvette Z06 and M3 E46), MR (the Hommell Berlinette R/S coupe has been a suprise to me... I never heard of it and from what time I was able to drive it, it's a car I found fun to drive with

...) and I was able to get by a chance of fluke a 'zero-counter' (well the wheel registered on replay almost no countersteering, very mild counter at best...didn't realize it till I saw the replay...) on Tusukaba (sorry for miss-spelling that too) on the very last corner with an R33 GTR, which is AWD.
In a sense, AWD's are easier, but on a fundamental level far as I know. To learn how to drift a 4WD could be either very easy or terrifing depending on just how you're trained, driving technique wise.
I'm used to countersteering and throttle control to some extent, it's difficult for me to turn off that impusle to countersteer and to let off or feather the throttle thru drifting as opposed to holding on full throttle and them some. A guy like Swift or DR would be able to explain it better.
For me, though FR is harder on paper, for me it's easier, maybe on the fact I know how to do it more so than AWD.
Though it's also to personal opinion and prefrence and whatnot. It's easier in essence to use a 4WD but 4WD has it's limits in it's own right. I've found for me at the least, I don't feel as 'free' or lose as you would in an RWD, it must have to do with the behavior of them becuase the spinning front tires help in taking care of the necessary of 'countersteering' as you would in an RWD car. I feel I have to be 'perfect' with planing a drift more so in a 4WD than an FR becuase I have to blance under and oversteering with such cars. But then agian I'm not used still to GT4 (I doubt even for grip driving a 2:30: something on Suzuka full with a Z06 Crovette on comfort tires would register as too quick either...)... but that's my view anywho.
Not sure what else to say.
Till later.