I think in 3.0 Ranger got the "Polymorph Self" spell (they were broken up back then). That alone would make it a decent melee choice at higher levels once it got access.
Cleric is probably the best choice. Druid less so...Natural Spell was not core in 3.0, so you have to choose combat buffs or spellcasting, on top of waiting several levels to replace your physical stats (you know...dumping them in anticipation of wild shape hurts at low levels). Cleric never has to make any of those hard choices, even in core 3.0, he just may need a round or two of buffing before starting his onslaught.
EDIT: IIRC, 3.0 monk's flurry progression was completely divorced from BAB just like how Pathfailure had it before their errata, so multiclassing monk with ANYTHING is stupid unless you aren't planning on using flurry anyway.
Oh! Also, 3.0 was the Haste-Harm-Heal edition. Haste gave extra standard actions, Harm was instant death, and Heal was a literal full heal (and instant death to undead). Those three spells were regularly cited as being the most overpowered in the game. So you want someone who can cast some or all of them. Even more reason to be a cleric or a wizard or sorc instead of druid. Buffs like Fly also had much longer durations in 3.0.
