well it depends on what you're looking at doing, as i understand it
a shorter focal length gives more depth of field but less working distance
and a longer focal length gives less depth of field and more working distance,
more depth of field is nice since that much more is in focus
but more working distance is nice when you don't want to scare the object you are photographing
another thing to consider is vibration reduction/compensation or optical/image stablizers (many brand names for vibration reduction), they'll make the lens cost more by quite a bit but will allow you to work with less light better
personally i own a tamron 90mm macro lens f/2.8. no vibration reduction but costs about $400 less then the nikon 105mm vr lens
and 90mm is the inbetween for macro focal lengths
short ones are 50mm or so, medium length being 90-105mm and long being 150-180mm or so
as for brands overall i there's obviously considering if you have a nikon or a canon camera, and then third party lenses, i think the top brands from what i've read are Tamron, Sigma and Tokina.
hope this helps
