First off, I advocate using the Qbanks rather than the Qbooks as they are more up-to-date and it is much easier to track which subjects you are weak in as they provide pretty good statistics on what questions you have answered correctly/wrongly.

If you have the time, definitely do all 3 Qbanks that I have listed in this list (there are others but these 3 are the best I feel and each bring a little something different to the table):
- UWorld
- USMLE Rx
- Kaplan

If you only have time for 1 Qbank, use UWorld
If you have time for 2 Qbanks, use UWorld and something else:
- If you are weak in first aid details: USMLE-Rx
- If you know first aid pretty well and want to challenge yourself/expand your knowledge beyond only high yield material: Kaplan

The advantage of USMLE Rx is that it really helps to reinforce high yield details from first aid so if you are having trouble remembering the details this is definitely the Qbank to use.