I am a pro-real-fruit kind of guy. I think they add the best flavor (in my experience). Fruit will add different characteristics when introduced at different times. For example, if you want your raspberry wheat to retain the raspberry sweet-tart nuance and be able to taste a "raspberry" taste, I would suggest racking onto a bed of raspeberries in your secondary fermenter.
If you want more of the tart flavor, to add a tart or crisp dimension to the finish of the beer, I suggest adding the fruit at flame-out of your boil.
If you want a balance between the two, add it to your primary.
In my Razzmatazz Weiß I use 6 lbs of fresh raspberries for 5 gallons, this is way too much if you are looking for a more "regular" weiß. I would suggest around 3 lbs of fresh raspberries for a 5g batch added to the secondary.
Also, after the fruit turns all white, wait an extra 2 days, then rack to a tertiary fermenter for clearing. I would give it at least a month in the tertiary fermenter before bottling to allow the flavors to properly meld and give it some time to bulk age.
Good luck, and tell us how it goes!