best close focus adapter

I am going to be at a butterfly house on my vacation next week, and I was wondering what my best option would be for adapting my 85 to close focus duties? Should I go with tubes (12 or 25mm), or is a diopter my best bet? Would I be better adapting the 70-200? I didn't really want to spend a lot, since I rarely ever shoot macro.

Thanks in advance

voited for the dioptre on the 85 without knowing the lens, you really want 68mm set of tubes.

Anybody else have a suggestion?

Tubes give the most magnification with shorter lenses, and close up lenses give the most with longer lenses. You may not find a decent 77mm close up lens however, and you will not like the results from single element lenses such as Hoya, Vivitar etc. You may be limited therefore to 58mm, which you can stick on your 85mm. If this is the route youtake, choose a multi-element lens by Canon, Nikon etc.
But tubes may be a better bet as adding even a minimum number of tube(s) means you can choose different lenses for different magnifications. At least in a butterfly house, the exhibits are used to people so you shouldn't have too much trouble getting close. Don't forget to post some pics here.