RE: Split muscles?
You can do either routine split as long as you have the right amount of rest in between each workout. for routine 1, I would have workout 3 in between workout 1 and 2. that so your legs can recover from back properly and vice versa. FOr your second routine, I would split that into 4 workout days.
I like the first routine better, because I like working complimentary muscle together for optimal recovery. But thats my preference.