We've done a couple of holidays with TA and generally been very happy indeed. Their trail knowledge is superb – you *could* get by without a guide, but you'd waste a lot of time figuring stuff out for yourself. Add in full board and lodging and it's actually a relatively cost efficient way to guarantee a really good holiday.
I actually preferred Les Arcs to Whistler. Less stunts and airtime, sure, but there's not the whole forced "americanness" feeling, and a lot of the trails over on the northern face of the hills really reminded me of The Shore and Squamish, especially in the wet. The network of lifts also means that an awful lot more terrain is open to you without needing 4×4 uplifts which just eat into riding time.
TA do run multiple groups every day to cater for different skill levels and riding styles – all gravitationally inclined though! Trails like Lavarda, beautiful though the scenery is aren't for everybody. One rider in our group this year had a bit of a hissy fit because they simply couldn't cope with the sustained technicality of it.
Any bike with big forks (but not triples) big brakes and big tyres will be perfect. Ash one of the TA directors has just got a 5, which says it all really…