I'm just going to say that /rdm is the only subjob you will need for the vast majority of the game.
/whm is meh unless you need to cure a lot of status effects between nukes
/blm is nice when you need to sleepga a lot or stun is important
maybe some odd things like /thf or /nin, but these would be highly situational
But honestly /rdm is the sub I use almost exclusively.
Scholar isn't near as dependent on it's sub as it use to be. In the most current update they gave scholar blink, stoneskin, and aquaveil. Those three spells are what made /whm and /rdm so attractive.
The other big advantages for redmage sub is that it gives as much magic defensive bonus as whitemage, as much magic attack bonus as black mage, fast cast, and convert. It also gives access to the vast majority of enfeebling magic in the game, which scholar is sorely lacking. It's just a nice all around sub that compliments scholar well.
Edited, Dec 23rd 2010 7:23pm by Ahrana