Pros for fish only: Not limited to choice of fish; no lighting worries; fish are more forgiving of less than perfect water (though of course on the other hand this might tempt us to keep it less than perfect); no worries about supplements of calcium, trace elements, etc.
Pros of reef: It looks a zillion times better! There's no tank like a reef tank! A bigger challenge, if you like challenges. All the live rock and little critters provide all the filtration you need (apart from the skimmer) and you don't get a nitrate build up. More natural environment for the fish, and they look happier.
I've kept both and if I had another marine tank it would have to be reef - every time!