What do you want the top reward to be?
Mount is fine but there should also be a completely unique pvp set shell for the top, special weapon shell, maybe even animated or color changing. All you Jedi and Sith with a color changing light saber crystal. :P Pistols, rifles, cannons with color changing laser targetting. Maybe even some unique emotes. Pvpers love their freaking emotes let me tell you. :P Increased com cap. Pvp non-combat pets. Unique pvp companion. Ability to have an arena in your player-custom house.
What do you want the middle rewards to be?
Pvp weapon shell. Emotes. Increased com cap. Unique pvp companion.
What do you want the lowest reward to be?
Extra coms. Unique pvp companion.
The companion could maybe give you your dailies automatically and talk about past pvp battles and stuff.
One season would be an arena droid, then an arena-wampa, then others, but if it was a trandosian or wookie they need to be very different from the current ones or at least completely different, very very arena-looking customizations. Dirty, burnt, defiant, tough mo-fo's. Maybe even make a way to duel with them. Like Proxy from Force Unleashed...