I like all star treks. If star trek is on chances are i will probably watch it. This being playoff season and all however haven't watched one this week.
Making a hierarchical taxonomy of my favorite series would look like the following
TNG- Of course Picard is a bad ass mother@#$ and I like the interactions between Worf and his human counterparts.
TOS - Simply because it's what started it all. Everything in Star trek derives form it.
Voyager - I like voyager over DS9 becasue of the fact that they are on a ship actually moving and exploring (even though they're lost) and meeting new races.
DS9 - loved it again especially for Worf and how he falls in love with that girl (As you can see i dont watch the shows too often)
Enterprise - have watched ONE episode in my entire life, will never watch another one.
Now if i had to do the same with movies it would go something like this.
1st - Generations
2nd - The Undiscovered Country (as you can tell i like the klingons)
3rd - First Contact
4th - and Ironically the fourth movie - The voyage home
5 - The wrath of Khan
6 - Final Frontier
7 - Search for Spock
8 - TMP
9 - Nemesis
10 - Insurection