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I never did answer the original question here because there are too many classes for which there is no single edition I though was best. Since this has generated a lot of posts, I'll go ahead and take a stab at it. The common theme here for me is that 4e is good if your plans for your character line up neatly with one of the roles/specalties in 4e, but it often didn't work well when your concept didn't fall into one of those narrow channels.

Bard - 4e plays better if the class's focus on arcane healing+other stuff suits your character, but the 3e version is easier to use in other ways.

Cleric - 2e was best for theme if there was a specialty priest that suited your character, 3e if there wasn't. 4e did the best job of letting a cleric be a healer and stilll do something else but had little support for non-healing oriented clerics. I consider all versions decently playable here.

Druid - I think 3e was best if the DM kept the player from abusing the feat options for druids.

Fighter - 3e was in the right area conceptually but played badly in practice at mid/high level. 4e was good if you wanted a defender fighter but bad for everything else. Slayer was good if you wanted a big two handed weapon and came along way to late.

Monk - 4e seems to play best in practice. Monk is well suited to skirmishing striker and most other versions are best described as a random pile of odd abilities.

Ranger - 2e was better then 3e, but mostly because of 3e's weapon specialty focus that really limited Rangers to a few weapon combinations. 4e's ranger was good delivery platform for dual weild and ranged strikers but nothing else.

Rogue - 4e was best if you wanted a skirmishing striker, bordering on being OP, but 3e was better if you wanted to do something else with your rogue.

Wizard - 3e really stripped too many of the restrictions of wizards without adjusting the spells to match, so 2e plays better in practice. The 4e wizard is an OK area controller but is really deserves a new name because it was effectively unrelated to wizards from older editions.

Majority Classes

These are classes that have appeared in three or more editions (not including the playtest).  Results in boldface beat its nearest competition by double. 

Class	BECMI	1e	2e	3e/PF	4e	Playtest
Assassin	0	0	4	1	3	0
Barbarian	0	7	10½	2½	17	1
Bard	0	2	7	8	12	0
Cleric	0	0	12½	6½	12	7
Druid	0	8	9½	5	3½	0
Fighter	2	3	4	7½	20½	1
Monk	0	7	1	5	14	1
Paladin	0	3	7½	13½	13	0
Psion	0	1	2	3	1	0
Ranger	0	7	7½	5½	9	0
Rogue	0	2½	6½	9½	16½	1
Wizard	1	6	12	3	6½	1

Minority Class Concepts

These are class concepts that have appeared in various forms but not in one consistent form more than two editions (not including the playtest).

Class	BECMI	1e	2e	3e/PF	4e	Playtest
Artificer (or any item-enchanting class)	0	0	1	4	1	0
Avenger (or any dextrous divine class)	0	0	1	0	3	0
Gish (elf, swordmage, swordsage)	2	0	0	1	1	0
Shaman (or other primal non-druid classes)	0	0	2	0	2	0
Sorcerer (or other non-Vancian arcane casters)	0	0	0	7	6	1
Warlock (or other blaster wizardly types)	0	0	2	12½	13½	1
Marshal/Warlord (or other martial leader types)	0	0	0	4	18	0

Updated!

Majority Classes

These are classes that have appeared in three or more editions (not including the playtest).  Results in boldface beat its nearest competition by double. 

Class	BECMI	1e	2e	3e/PF	4e	Playtest
Assassin	0	0	4	1	4	0
Barbarian	0	7	10½	2½	18	1
Bard	0	2	8	8	12	0
Cleric	0	0	13½	6½	12	7
Druid	0	8	10½	5	3½	0
Fighter	2	3	4	7½	21½	1
Monk	0	7	1	5	15	1
Paladin	0	3	7½	13½	14	0
Psion	0	1	2	3	1	0
Ranger	0	7	7½	5½	9	0
Rogue	0	2½	6½	9½	17½	1
Wizard	1	6	12	3	7½	1

Minority Class Concepts

These are class concepts that have appeared in various forms but not in one consistent form more than two editions (not including the playtest).

Class	BECMI	1e	2e	3e/PF	4e	Playtest
Artificer (or any item-enchanting class)	0	0	1	4	1	0
Avenger (or any dextrous divine class)	0	0	1	0	3	0
Gish (elf, swordmage, swordsage)	2	0	0	2	1	0
Shaman (or other primal non-druid classes)	0	0	2	0	2	0
Sorcerer (or other non-Vancian arcane casters)	0	0	0	7	6	1
Warlock (or other blaster wizardly types)	0	0	2	12½	13½	1
Marshal/Warlord (or other martial leader types)	0	0	0	4	18	0

Updated!