Retiring at 31 is trivially more efficient in terms of XP per loom (a few hundred thousand, I believe), but I definitely prefer retiring at 32.
You spend half as much time as a useless peasant and instead get to spend that time playing with a nicely filled out build... and you get 2 looms + gold to buy your next item!
The downside is that you won't stack up the retirement XP bonus quite as fast, but I'll sacrifice efficiency in the name of fun any day of the week.
(I'm around gen 11-12 right now, and haven't looked back since starting L32 Retirements at gen 5-6)