Ranger -- everything is easy to do alone -- Training is fairly easy as there are several areas you can stand and kill monsters and not have the monsters mob/hit you. Leveling is fast as well. Make sure to have your base stats: 18 dex, 15 con.
Second option is Warrior: You can solo train, but at early levels (1-18), it's a little difficult. You would need a mage. From 19-25, you can solo train, it'll just take a lot of potions/food items. When you're heading into desert areas for training, or sky maps, you will need a mage (but you can always just PT a low lvl mage so your EXP gain from each kill doesn't vary much vs soloing alone).
