Personally I would go with the bar. The thing about the machines is they just dont let your body move naturally.
Just be sure and go light with high reps as in 20 reps sets. Also for a warm up I use just body weight squats and really watch my form. I typically do from 3-5 sets pending on how much I feel I need, This follow 10 min on the bike.
Let me know gurl and KTS!!