I have been jusing Jefit - it's OK. It works, but is not exactly perfect for me. It lacks a lot of stuff for tracking intensity increasing strategies, like drop sets, forced reps, etc. It also is a little annoying because you cannot differentiate between a warm up and a working set in an exercise; but my workaround for this is to create a custom exercise for each exercise that I do warm ups on. For instance - it has bench presses and I will make a custom exercise called "Bench presses - warm up" .
If you don't do this, it calculates your 1RM and prior performance based off your working sets and then the next week you go to do your warm up and it has all the info from your working sets. Example:
Bench Press
15 reps X 135 warm up
6 X 200 set
5 X 200 set
4 X 200 set
Then when you come back next week it will have the chart filled out like:
4 X 200
4 X 200
4 X 200
4 X 200
Or something like that - and you have to modify the weights for the warm up, etc. It's minor but it's kind of a pain when you're in the middle of a workout.
It does have a stopwatch built in to monitor rest between sets, which I have found very helpful.