I started with Warrior because of its specialty in weaponary. But I usually play as Solo so it's very tough for me (Warrior 8 after 24 hours of playing the game but gaining level after 8 is hard). So I decided to change Red Mage.
With Red Mage, I have my magic to support me and help other players that I see around.
I also, sometime play with a Level 42 Red Mage. This player is from Japan and I'm from California. So, it's hard to play together because of huge time different.
Any way, that Red Mage is not bad at all, 604HP/300MP and she got some good Equipment as well. Also have some on Auction for 13,000s.
And with Convert, she can switch HP and MP to cast a lot of magic....
My Sub is probably going to be Black Mage. Since with Red, I'll have decent support magic, so, I'll need good attack.
From my experience of playing all previous FF games, I must say this; I always start the game depend on Melee but at later of the game, I always depend on Magic. Because of this, I might switch to Black/White later on.