Well, you should use both if you have the capability. Use the dynamic up close to capture all those tasty transients :D Then Use the Condenser at 3 or 6 feet away from the cab to capture a dynamically "flatter' track and blend them. Lovely.

About the feedback. Turn the gain down. Nobody has gotten good results using 'gig gain'. When you layer the parts having the gain too high will cause the mix to sound muddy and you'll actually lose the tonality of the whole rhythm section. Plus, crank the volume, not the gain 8-)

Mic choice and placement will yield widely varying results. You might want to read and listen (there are a number of wav. files linked to this) to this article from Sound on Sound Magazine.
http://www.soundonsound.com/sos/aug07/articles/guitaramprecording.htm
It compares condensers/dynamics, placements and blending multiple mic options.
When you say feedback is this from the amp itself or from the recording process? In other words does the feedback only occur when you are recording?
While I agree with GF that lower gain settings than those you use live will yield better recordings as a general rule, I disagree with raising the volume. Lower gain and volume in general will yield better recordings.

Audix has a short video on the subject. Their products are prominently featured, of course, but the video has a lot of info that doesn't depend on that.

If you've got the time to read it, Slips has a great tutorial over here:

http://thewombforums.com/showthread.php?t=3173

Feedback

It seems like the other boys have answered the other parts of your questions - but the one thing I think is important to remember is that if the amp is feeding back (because of distortion or proximity) then it will be in the recording.

Sometimes it's a simple as having the player stand back a certain distance, sometimes you need to put the player (or the amp) in an isolated room. That being said, sometimes you really want the feedback - and then you just let 'er rip!