I have one of each. Both from Bendpak. My primary concern when I got the 4 post was storage for the Cobra. With that being said I don't even consider putting the Cobra on the 2 post when I have any maintaining to do. I have the pneumatic jack on the 4 post that slides between the wheels and makes it extremely easy to get the wheels off the ramps. The only thing that gets a little more complicated is if I need to get all 4 wheels airborne at once. I have the HD9 series 4 post and the width between the ramps is wide enough that everything is accessible under the car. The wheels sit on the ramps with about an inch to spare to the inside of each wheel. Once the car is built I would say the 4 post allows easiest access to everything.
To get the Cobra on the two post I would have to first raise the car enough for the arms to swing underneath the side pipes. That adds another step to getting the car lifted vs just driving it up on the ramps of the 4 posts.

As far as the ability to move the lift ask yourself how much you will actually want to move it. I have moved mine once and that was just because I was installing race deck flooring and needed to get the pieces under the corner post. Even on the castors it is a pain to move and you can only move it so far from your 220V source anyways. Of course 110v is an option on some lifts, bendpak included. If you do anticipate moving yours around you may consider a 110v motor. Only drawback is it goes twice as slow but that is only on raising it because it essentially gravity descends. Only uses the motor going up.