I've used all of the above and have owned 2 Millers and 1 Sullivan.
I like them in this order:
1. Miller - Similar to the Astro. Recessed button. High quality silicone rubber inserts with replacements available; wont burn marks into plastic spinners. Very good customer service. My first one had the older switch that gave out after 3 years of steady use. I called Miller to buy a new one and they said they would repair the original for free. I didn't feel like shipping it back and figured that I had gotten my money's worth already, so I paid for a new one.

2. Astro Flight

3. Lite Machines/Norvel

4. Sullivan Cricket - The bearings overheated on mine after a few weeks, but I may have had a dud. Not as nice feel and switch as the others listed.

The Sullivan and Astro Flight are the smallest, but they all use the same size motor. They are all too powerful for anything under an .049.

Check out this thread for a simple, home made .020 starter.
http://www.rcuniverse.com/forum/fb.asp?m=2011857