WELCOME ABOARD!
Here are some of the things I've said about them in the past:
http://www.subsim.com/radioroom/show...10&postcount=5
http://www.subsim.com/radioroom/show...39&postcount=4
I don't have time to go over all the differences right now, since I have to post from the library and only have an hour to cover all of Subsim, but if your question hasn't been answered by next week when I'm back online for real, I'll give you a full rundown. The differences are many.
On the other hand both are very cheap right now, so there's no reason not to buy both and find out for yourself.