Basically I think different people will have different feeling about the difficulty of these two companies. AFAIK, Uber's hiring bar is as high as other top companies like Google, Facebook etc. and the interview process is quite similar.

That being said, you are mostly expected to have general coding questions that focus on data structure, algorithm, system design, testing and so on. In terms of differences, I think Uber interview cares more about culture fit and interviewers expect candidate have great passion about the company and its mission.

I think in general the preparation process for these two companies can be exactly the same as general coding interview is very standard.