I use the Sigma 105 for almost all my photography - only using my Nikon 60 Micro for larger objects like paintings, etc. For flora and bugs, the 105 will give you a pleasant distance to not spook the bugs, and a little room to bring in anything from a reflector surface (reflector, foamcore, mirrors, white inkjet paper - whatever) to a flash or strobe.

(attached shot taken with the 105)

How much room do you have for portraits? Do you have a studio, or do you think it will be in confined areas - this is where the 60mm (or 50 in your case) would come in handy.

This is a one of those "you don't actually know what you'll need until you are there" decisions. I love the shallow DOF from the 105, and I find the flattened field more flattering for portraits, but this is MY opinion. Some people can't get enough of ultra-wide lenses for portraits - get it?

Whaddaya like?
-Lew

Go into a camera store and try some out - see whatcha think. Macro (true ones - not a typical zoom that has the word "macro" as part of its name) lenses will more often than not give you a 1:1 ratio, so you're covered there as far as how big can you get it in the frame - no difference.