There's a great BYO article here that I reference quite a bit when making fruit beers. I find I prefer natural fruit over extracts as the flavor has a bit more depth and subtlety than extracts that seem to taste a little one dimensional and artificial. The downside to real fruit, though, is the risk of infection, tannin extraction and more work/time to make it properly.
Extracts are convenient and eliminate most if not all infection sources and you can simply add them at bottling, but the concentrated flavor makes it easy to use too much so be sure to add maybe 1 tsp at a time, taste and add more until you like what you have. You can always add more, but you can't take it back once it's in there.