I think your best man needs to have five great qualities:
1. Reliability. Will he be there to help you when you need him?
2. Does he know you well? Will he know what kind of Stag Party you will actually enjoy? Can he make a speech with depth, not just tell jokes at your expense?
3. Responsible. Can he be left alone to arrange a group of men to go on the Stag Party and manage the Ushers on the big day? Will he lose your rings?
4. Diplomacy. Will he keep everyone happy especially your bride and her parents?
5. Confidence. Can he stand up in front of your friends and family (sober) and make a memorable, funny and meaningful speech?
If you still cannot decide who it should be, ask your wife. She may not get it completely right but if it’s her decision, you can’t get it wrong.