As a tank you have the bonus of being able to take the group at your own pace. Don't feel pressured to go quickly if you don't want to. If you want to just get used to the dungeons then a dps is probably best. However from my personal experience the game felt much more enjoyable once I began tanking.

As for the ranged vs melee debate. Do whats fun, not whats best. Find what feels good to you and go with it. Survival can just come down to learning ways to avoid taking damage and using a chocobo.