Firstly: Getting a sponsor isn't like getting married - it's not a lifelong committment. Don't sweat it too much.
If things don't work out, find another. Switching sponsors isn't an insult to anyone.
Other than the above, here's my criteria:
1. Someone who has what I want.
2. Same sex.
3. 2 or more years of continuous sobriety.
4. Actively works the 12 steps.