The best army to play with is the one you like the models the most of.
There are actually 2 questions here:
1) What codex do I like the most?
2) What codex can make the nastiest 600pt army?
Which one?
I'm all in favour of:
Farseer: Guide.
3 Jetbikes, Shuricannon
3 Jetbikes
Warp Hunter
Warp Hunter
Warp Hunter
597pts.