Both have their individual attributes and I don't see any reason why you should need to select one or the other - you can do both! 
I love 5 min blitz on FICS. It can be a great rush and gets that adrenalin pumping in time scrambles. Plus with your opponent having less time to calculate, often the door will open for some amazing sacrificial combinations - which are a great pleasure when they come off. The clock adds a dimension to the game and a whole new set of skills and tricks need to be learnt.
Correspondence chess can be seen as more of a learning exercise and an unhurried way of enjoying the game. I do agree that the lack of continuity can detract from the experience but in blitz the greater frequency of blunders and the fact that you can lose on time can detract too.
Hi - does anyone agree that the 3-day limit on moves is both good and bad? Good, because it gives us all time to fit a game in around our schedules. Bad, because you don't always have a fluent, focused game. I wonder if speed chess, or a game where you have no more than five minutes to make a move, might be a good option to choose? Any thoughts, anyone?