Of the 'main' cast...

1. Jin
2. Richard
3. Miles
4. Hurley
5. Eko
6. Daniel

Those six constantly change order for me, although I think Jin remains #1 throughout. Claire & Sun the best of the girls.

Of the 'supporting' cast... (in no order this time, as I don't know which I like better )

Keamy
Rose
Tom
Widmore
Mikhail