Best rep range for fat loss/muscle building

For the most part, you can't do both at the same time. Stick to your weight loss plan and choose a progressive lifting program that will help you maintain muscle mass as you lose.http://community.myfitnesspal.com/en/discussion/10332083/which-lifting-program-is-the-best-for-you

I used old school 3x5 and 5x5 routines to get to a 1150lb total. After that I switched to cube method ( has a mixture of low rep ranges and high, thing 1 rep to 12 rep sets). Once I switched to cube I progressed to over a 1400lb total within 5 months.

I switched back to lower volume training for cutting down from 250lbs. Big mistake. Low volume, lower rep training really saps the central nervous system AND recovery for the body is harder than higher rep training. So while "reps don't affect fat loss", they definitely affect your ability to stay on track.

Personally, I find 8x8 squats @ 55% 1 rm with 45 second rests easier on a calorie deficit than 3x5 squats @ 85-90% 1 rm with 3 min rests. It allows me to lift more total weight while giving my body a chance to recover. I've noticed that while I lose strength from not constantly training in lower rep ranges, the LBM is retained far more effectively than using lower reps during a deficit.

However, if this is your first time lifting, it doesn't really matter which scheme you choose. Your body will be eager to adapt to anything for at least 12 weeks before you need to really worry. Just get the fundamental movements in like squats, press, and deadlift after you have the mobility to do so.