BECMI: Elf. I've always loved fighter/magic users as an archetype, and when I started playing I thought elves were the coolest guys in the world. I'm embarrassed to say that my first ever character was named Elrond Half-elven.
1e: Paladin. Kick-ass holy warriors with awesome powers. Especially when Unearthed Arcana came out. My other favorite 1e class was the Psionicist from Dragon magazine (I was a big Deryni buff).
2e: Fighter/Wizards or Specialty Priests.
3e: Wizards.
3.5E: Psions. I loved druids, and played several of them, but I think my favorite class was the Psion. The psionic rules offered a flexibility that I loved, allowing me to come up with creative solutions to problems.
Arcana Unearthed/Evolved: Magister, for the same reasons why I loved the 3.5 Psion.
4e: Fighter or Bard, probably. I don't really have a favorite class in 4e. But I like the fighter a lot, because it's the first purely mundane fighter that's been interesting to play, for me. I also really like the bard, because it's quite versatile, and has lots of powers that mess with opponents in interesting ways beyond just damaging them.
Overall, I like flexible, versatile characters. I don't like playing ultra-specialists, I like playing characters who are veritable swiss-army knives, able to do all sorts of things. I especially like being able to try creative, non-obvious solutions to difficult problems. That's the main reason why I liked playing spellcasters prior to 4e, though I also find supernatural power fun to play.