Witch Macro linse, 100mm or 180mm?

I'll been using a Canon EF 100mm Macro on my Canon 20D, but now I upgraded to 5DMkII and have a 180mm macro lens.

Shoud I use the 100mm or 180mm, the 180 have a longer(0,48) minimum focus distance. I have both lenses, but witch one

gives the best picture under water?

I always recommend the Sigma 150mm f2.8 macro lens coupled with the Canon 500D diopter. Also, please see my recent article about the Tamron 70-200 f2.8 macro zoom.

To answer your question, the 100mm is the best all-round lens for mid-sized fish etc and goes to 1:1. The longer lenses are good when used with a diopter for >1:1 shooting.

Cheers

James