When to reset DG

When should I reset my dg? I had a check mark from 12-25, and there wasnt an option for a level after 25 (I probably didnt unlock yet) so I reset my dg, was I suppose to?

You reset when you no longer gain prestige from doing a dungeon. Once you reach the highest attainable floor for your level and finish it, that is when you need to reset. Otherwise, you won't gain as much exp as you could for doing dungeons.

What if you had a really crappy last floor? Like 15 deaths on that floor, should you reset it, because the xp will carry over back down?
I have trouble trying to answer that question :S

Oh, so the prestige is based on a base number, not the total! Thanks!
And 15 deaths was an exaggeration :p

Prestige is based on the number of floors you complete. So if you complete 10 floors and reset, your prestige is 10. If after that you complete only 5 floors and reset, your prestige goes down to 5. The more levels you complete, the better your prestige. So you want to do as many floors as you can before resetting. The higher your prestige, the better exp you get. It's taken me a while to figure out, but I'm getting the hang of it. I've gone from 13 to 53 dungeoneering over break. It's not a bad skill, but I still don't believe it's a skill. It's still a minigame not matter how you look at it.

That match was unrelated, it was, "for fun", like I said.
We were dunging with a few people who ditched, and Earth and I just TP'd the place carelessly.