I usually don't have any problems with either one. Just blast the elbow with a very good propane or acetylene torch and it expands away from the pipe or the nipple. The pipe wrench extracts the nipple or removes the elbow from the remaining length of pipe.

Heat is my friend.........I'm never on the job without it. I recently bought a relatively costly propane torch (cast aluminum) with a 3200F. flame temperature. It's fantastic.