Rack pulls are great if you weakness is not off the floor but I find that alot of people once they switch back to regular pulls get less out of them than they thought.
I like to do pulls off of boards, I get some sheets of 3/4" plywood and stack them to what ever height I want to work and pull off them or I use the jumpstretch band and do reverse band deadlifts. I feel these are much better in my opinion than rack pulls because: 1. you use a full range of motion
2. you don't mess up the groove of the pull
3. You can overload different points of of the lift depending on how you set up the bands and what kinds of bands you use. i.e. I usually use the green bands, I set them up(in the power rack) so that the bands totally deload when the bar reaches mid to upper thigh. the bands at floor level take about 75lbs off the bar. so if you max is 500 if you put the bands on you are pulling 425 off the floor and locking out 500, you can usually go well beyond you max using this method.
4. I find that using the bands this way builds explosiveness/speed off the floor. you have to be fast to be able to lock out the heavier wts at the top. If you are slow you will not get the wt.
5. you can use board with the bands as well to get a greater range of motion.
hope that helps.