Ya know, its a tough decision, but I think my recommendation is to go with the largest size mill you can, for the money you want to spend. I say that because you can do small work on a larger mill, but you CAN'T do bigger work on a small mill. I actually have two mills, one is a larger benchtop, with a 2hp motor, and R8 spindle. I also have a floor model Grizzly that has a 40" table.
I've had two of the "micro mills" in the past, and was very disappointed in both of them. A 1/8" milling cutter was pushing their capacity, and even for something like slotting guards I felt they were just not up to the task.
Something like this is the minimum I would recommend:
http://www.grizzly.com/products/Mill-Drill/G3358
That is very similar to my smaller mill, and this is the larger one I own:
http://www.grizzly.com/products/Vertical-Mill/G3616