A dynamic mic is essentially a speaker in reverse, a condenser uses a charged membrane.
Really good mics of each category can give you really good but different results when used properly. In general the worst condensers are a little better than the worst dynamics.
The best really newbie analogy that I can give are those two-sided bathroom mirrors, with a regular side and the magnifying side. Which side is better? Most condensers are a bit like the magnifying side. You see a lot more small details with them, but if those small details are not pretty then it may not be as attractive an image as the non-magnified side.