Well,

I've used both and saw no difference in performance at all. Even in the same airframe. The Dynamax fan is built better, IMHO, and, depending on the airframe, can be less of a hassle to install. Jedi, you're right, the Ramtec is a hair bigger, so if you've got certain airframes (like the Y/A F-18 single, for example) you'll have a hassle getting it in and out.

Go for the Dynamax.