Only two rules: 1. Must be widely avaiable. 2. NO CORN SYRUP!
Here are my three current favorites in order of preference:
1. Drew's Organic (medium)--It just tastes fresher.
2. Harris Teeter H.T. Traders Chilpotle (medium)--Nice blend of smoke and spice.
3. Newman's Tequila Lime (only comes in mild, darn it)--A tad bland but makes up for it with a nice citrus kick.