To be fair you may want to have at least one of every role. in the long run it will become more helpful specially if your going to do end game raiding.

I would recommend PLD ( easy to learn )

DPS I'm a DRg at heart however NIN is fun and a lot like MNK

For range I'm more of a BLM , however if you like support RDM is fun.

Healer Many like SCH I'm more of a AST I like the challenge of boosting / managing the buffs.

Over all just make sure your having fun.