Adam, I've been exactly where you're at. I struggled quite a bit to make my decision, and the people here were very helpful (and open minded) with guiding me towards info that I used to make my decision.
I originally decided on the Micromark equipment, and ended up changing my mind and buying Sherline. I am very happy with the Sherline equip. For me the factors were:
Micromark:
+ more capacity and rigidity (as you note)... just seems more robust and able to do more/bigger stuff. One never knows when I'll need to lathe up something big!!
- import costs (I'm in Canada)
- shipping costs
- weight (not really portable)
Sherline:
+ portability. I have it beside my workbench, and just move it up/down whenever I want to use it. I know now that I would have been frustrated going upstairs/outside to the garage everytime I wanted to machine something...
+ accessories
- capacity (although this is misleading. This little monster is a lot more powerful and capable than it looks.)
- cost (for you, I expect the cost of the Sherline will be more, but for me, they were about the same)
There's lots more factors, but those are the ones that guided my decision. My money, therefore, my decision. There's all sorts of debates all over other forums about what's better, but as long as you're machining, and your happy, then you will be fine. Regardless of the choice, there are LOTS of online users of both brands/styles that you should easily be able to connect with others for tips/tricks on things.
Also, check out Taig. I've read quite a bit about them, and they are worth consideration. Similar size to Sherline, but less $.
Let me be clear though.... I'm a major beginner in all of this stuff, so there are others here that will give you far better and more thorough advice than I. I just found your post interesting, because it captured my same ideas/thoughts from several months ago...
Check the other threads here, there are lots of links and threads with things that will help you make your decision.
Murray