Wow, sounds like you've been doing some shopping.
Get rid of the extra 50, they are just dead weight. Do some test shooting and figure out which one is sharper (or look at a site like photodo.com).
I might lean towards one of the following (in order of preference) -
1. a good solid tripod. If you don't have one of these, I would move it to the top of the list. A flimsy tripod is almost worse than none. Heavy is good. I really like Bogen tripods.
2. a flash and off camera cable. Having the ability to add a little fill flash and vary the position of the light is very valuable for macro photography.
3. a long telephoto. I might be inclined to look for a good 300 or 400 mm lens. Some of them even have limited macro ability (1:4 or 1:6 is usually it). Sometimes these can get you shots of flighty herps (lizards or frogs) that you couldn't get otherwise.
4. a good macro in the 90 to 105 mm range. There are some excellent lenses out there and this is a great herp lens. Get one that goes 1:1.
5. a good telephoto 1:1 macro can be nice as well. Here I would look for a 180mm or 200mm macro. Pricey, but worth it.
-----
Chris Harrison