Why would you want to be less confrontational in an interview? The point is to see if the candidate is good or not, not "let's see how I can ask this question in the nicest way possible so I can get a nice and safe response that the candidate will just read off his / her resume".

The fact is this question weeds out people who truly havent' done anything difficult or unable to communicate their achievements properly. If you have an impressive set of skill / strength, then it should be easy enough for you to pick one.

In my mind the question forces the candidate to show the interviewer his / her:

1) Communication skills (i.e, is this person going to tell me all their problems, or just the one major problem that he/she needs help with)

2) What they view as an accomplishment or challenge

3) How they handle challenges

4) Their ambition (i.e, did they take a leadership position in their accomplishment or did they sit back and let everyone lead the project)