I have an aluminium and a composite XTC29er and I can thoroughly recommend them. I’m having to sell the composite frame (long story), but I’ve found that both are a really superb blend of speed, comfort and manouverability – they’re great fun for trail centre shenanigins!
If you can stretch to the composite, I’d recommend it, as it’s hugely stiff under acceleration, but really vibration reducing through the pedals when descending (for a hardtail!) Only thing to watch on full builds is some of the bits they hang off the frames to get overall cost down.
p.s. if you are interested (and are a medium in Giant frames!), I am selling my XTC29 composite frame – just drop me a line if you want more info.