For solo/survivability, I would suggest maining as arcanist/summoner, marauder, or archer.

Arcanist has access to a tanking pet (lvl 10), heals, and dots. The damage is slightly lackluster if you build MND, but INT as summoner is fairly speedy. Just be aware your damage potential is slow to start.

Marauder can be played as a tanky dps. You have some hp recovery abilities, but you will want to cross-class in to lancer for "blood for blood" for that extra hp recovery.

Archer can be a tanky dps as well (in a manner of speaking). DEX is both your damage and evade stat, so it works out nicely. Use hp recovery abilities and buffs from pugilist, Marauder, and lancer to round out your heal and tankiness.

Also consider dabbling in to conjurer for the ever-important "protect" buff and "cure" spell.

And you will have to join parties for almost all of the dungeons. The story requires you to participate in at least 9 dungeons and 3 primal fights, all of which requires a party. If you want to complete other aspects of the game, such as those related to GCs, you will also have to form parties for even more dungeons.

Alternatively, you can level up your crafting and gathering classes on your own with relative ease. It is one of the best ways to make money for future adventures, especially since endgame dungeon runs can cost more money (from repair costs) to run than you actually gain (because of wipes and such)