I won a Duel tournament with my Orochi just now. I actually won! That is not likely to ever happen again. I'm a good Orochi, not great, and a good player, not great. I know I got a bit lucky with my opponents.
I got an ornament reward of course... but not the one I want. In fact, I won't ever even use the one I got. I really, really, reeeeeally want the ninetails. I'm so disheartened by getting the diamond looking thingy (don't even care to check the name) that I don't want to play anymore. Especially since the Tourney can eat up so much time and at the very last second be without a reward.
Let us chose the ornament we want. Hell, let me trade this ugly diamond in.
At this time, there are no plans for players to be able to choose their rewards. The way the tournament rewards work, the rewards are given for the last hero you played and for the most recent season. So if you have not unlocked the Season 5 ornament, the game will look to give you that. If you already own it, then it will give you the Season 4 ornament. If you own both Season 5 and 4's ornaments, it will give you Season 3's.