I've been to both style of weddings - actually, buffet-style seem to be much more popular where I live. Out of 17 weddings, I've only been to four with a plated meal.
I LOVE buffet style dinners. For one thing, I'm quite small and just can't fit a lot of food into me! Plated meals often have a salad, soup, maybe another appie and then the full meal. By the time the entrie comes, I'm completely full and can't even touch it. I went to a plated meal wedding last year and my bf (who's 6 feet and over 200 lbs) couldn't even finish his meal. I didn't see a single empty plate being taken away.
So, with a buffet meal, there's a lot less food left on people's plates. Also, people can pick and choose things they don't like. If someone hates beans and you have beans on your plated meal, they'll be left. But if they're in a buffet, they just don't have to take them.
Another pro with the buffet meal is that the couple can do whatever they like with the leftovers! One of my friends donated the leftovers to a homeless shelter nearby, but most people take them home or share them with friends/family. A few of my friends used the leftovers for lunch the next day during the gift opening. I thought that was a great idea!
So, in all honesty I'd go with the buffet! My brother had a buffet that was *very* elegant and set up beautifully, so they can fit into a formal wedding very easily.