A lot has to do with your goals. From your comment I'm assuming it's weight loss and perhaps a part of rehab for your knee. The general rule of thumb for weight loss is to keep your reps between 8 and 12. I choose to go very heavy (and lower reps) but that's not necessary and given your knee, not recommended.
The best way I've found to torch the fat is to stick with the big compound exercises that work a lot of muscles at the same time: Deadlift, squats, bench and shoulder press.
Have you considered getting a trainer at least for a couple weeks to help speed up the "comfort" factor?
GW: 215 w/ <10% BF
Deadlift - 405lb - Goal: 500+
Squat - 375lb - Goal: 400+
Bench - 360lb - Goal: 225x30