Right now:
1. Mincoin - Because of its superior exchange
http://mcxnow.com - and because I like that it's scarce (only 1 million units in existence); good community, too
2. Litecoin - My first alt-coin - they say you never forget your first one
3. Powercoin - Because it's easy to mine, and I was able to start relatively early in the fair and pre-announced launch and because it has a fun community
Honourable mentions: BitBar, BBQCoins and Lolicoin (the upcoming, makes me laugh whenever I think about it).
From the future coins, the most interesting is Netcoin (MC2).