TOS - The original and the best. Lovable characters, fun, action and adventure in space.
TNG - Pretentious, self-important, PC, terrible direction, cardboard characters. Despite all that, a couple of great episodes here and there.
DS9 - Drab settings, whiny Bajorans, annoying Ferengi, Worf. Some nice space battles later.
VOY - Some likeable characters, an overload of technobabble, planet of the week.
ENT - Awful start, recycled planet of the week plots, then became awesome, fun and exciting when the Xindi came along.
nuTrek - The lovable characters of the original reinvented. Fun, action, adventure and spectacle like nothing before in Trek.
Novelverse - takes the cardboard characters and adds depth. Constant chaos and destruction since the Borg came.