I would say Kaplan is more like the real thing- long annoying obscure passages, much more likely to test you on random junk.
IMO UWorld is better for LEARNING. Questions are harder, stems are shorter, but the important thing is you learn a lot. Which i think is 95% of the fight.
I was satisfied with Kaplan until I tried World. I tried to go back to Kaplan but i couldn't stand it.
As I've mentioned before however, the kaplan biostats and WWJD questions are pretty good practice.