Arena Rank rewards: List of ranks can be found at the Arena Ranking rewards page.
In the Arena the higher Rank you are the more Prestige you recieve from all battles. and the Arena Rank rewards will be better also. Here it display the other player's Total Power, Level, and their PVP Rank.
A loss gives about half the gold, prestige and player experience as a win, so it's advisable to not climb so high on the ranking that there are no winnable battles left. (also note that the power drop from making your starter hero Adept and making the Adept Master can put you in this situation)
Defeating players ranked 1-5 earns 200 prestige and gold. Defeating players ranked 6-10 earns 180 prestige and gold.