I generally prefer long, integrated stories (I have reasonably good discipline about only watching one episode a night). Next Gen and SG-1 both occupy a nice middle ground, because even if the episodes are self-contained, they still engage in character development and reference previous events. Those shows are also nice in that manage to tell compelling stories without being overly melodramatic - so many shows now (especially sci-fi) are just re-skinned soap operas.

Watching shows like ST:TOS are painful for me now. That there is absolutely no connection from one episode to the next means that I have pretty much no investment in what happens. I only watched TOS just to complete the Star Trek lore, but in general I avoid such stories.