The rewards you get depend on the quality of the competitors?
The bonus you get is renown, and once you're at the top and earning renown, most characters will know you, and you'll likely get more of anything to do with renown...
If you're a regular tournament entrant, you'll end up with a ton of scalpels and ambassadors and kinght's falls and other bespoke weapons. If you time it right you'll end up with lots of 50+armour helmets too. Some are really good, and it speeds up kitting out your companions to the top tier.
In the end, all the effort in getting to the top mostly nets you hundreds of thousands worth of equipment that you can sell. It also really speeds up your skill acquisition...