Tripels can have some residual sugars in them if you don't ferment them all the way out. The Belgians are notorious for feeding them candi sugar additions in the secondary and using pasteur champagne yeast to dry them out and carbonate them. If you look at imported tripels from Europe, most use very thick bottles and a lot of them are even corked and caged like champagne. This is to prevent bottle bombs while the bottles condition. Gushing is sometimes a problem as well with all of the sugar additions.
Either method (keg or bottle) would be fine. I might suggest that you do both and see which you prefer. You might try some larger 350ml. bottles and bottle up about a case (12 bottles) and keg the rest. If you do bottle them, after you prime them, let them sit in a warm dark place for a minimum of about three weeks. If you pop one open after a week, expect it to come gushing out and any remaining beer to be completely flat. It takes time for the beer to absorb all of that CO2, so let them rest in the dark for three weeks and then put a test bottle in the fridge for a full day to cool down and absorb the CO2. Then crack it open.
If this is intended for competitions though, bottle them in strong looking longneck bottles, 12 oz..
