Leveling in swtor is one of the most enjoyable things to do. The story line is trully vast, interacticting with voice and options of choice and answers along your journey with each and every ncp while you travel.
Unfortunatly, your companions are only at worth while your leveling, and afterwards are only kept for crafting items for you, but they wont really be of any us other then that, since you will only be able to go into operations with players, and ofc you`ll be only use players to enter a warzone.
You can ofc use your companion in the outside world, but you will rarely encounter any opposing faction player to pvp with.
Mostly the storyline for each character is lovely, it shows your progression along the leveling, and now you become more powerfull after you overcome thougher enemys.