Early levels you probably want to focus on str and stam for the most part.
After you get high enough and gear becomes more available: str, stam, agi, crit, hit (not labeled in any particular order)
For leveling you'll probably want to use a 2h weapon until you are able to get a good amount of +hit gear, then you can dual wield or stick with 2h. Once you get to higher levels, make sure you have 1h + shield with you in case you need to tank something seriously.
Most likely it will be harder to solo level than to pair up with someone else. Warriors don't have good "Oh ****" abilities, like rogues vanish or hunters freeze traps and let my pet take the beating while I run away. Warriors will pretty much, put on a shield + hamstring + run away (and if you're lucky + intercept a rabbit or frog to gain distance quickly)
Personally I would rather party with a Priest over a Mage. Priest can deal damage and also heal you, unlike a mage who can only do dmg (of course they have slows, freeze enemy, polymorph, etc). When you have low hp you wont get some from a mage.
For leveling, like devioususer said, go Fury or Arms. Don't go protect even though you are going to tank with your partner. If you are taking too much damage just put on a 1h and shield and go into defensive stance. You'll be leveling too slowly (compared to Fury and Arms) in protection. I prefer to level with Fury; due to the Cruelty, Imp. Slam, Flurry, Imp. Whirlwind, and Bloodthirst.