I love a good hefeweizen! Franziskaner, Paulaner, and Weihenstephaner are excellent German ones that I can get around here.
As a German national (and beer drinker ) I can tell you that the differences between Paulaner, Franziskaner and Weihenstephaner are huge. Franziskaner is rich in flavour, has a full body and a quite noticeable smell and taste of banana juice, mixed with slight traces of citrus and a hint of clover. Franziskaner smells and tastes more streamlined and more restrained. Weihenstephaner, well, there are at least three versions of Weihenstephaner Hefeweizen, the dark, the regular and the stout, that they've named "Vitus." I'm excluding the Kristall, which has been filtered, so all the goodness (the yeast, which gives Weizenbier its special taste) has been removed. The dark Hefeweizen is good, the regular Hefeweizen acceptable, and I must admit I haven't tried "Vitus" yet.
However, as a local of the Rhineland - more specifically the area between Cologne and Düsseldorf - I prefer our local beers, of which there are a huge variety, and most of them are at least acceptable, some are good to very good and a few are even excellent. You will have trouble, however, finding them abroad. Very popular with the locals in Düsseldorf are Schlüssel, Uerige and Schumacher whereas Päffgen, Malzmühle and Früh are the favourite beers in Cologne, at least with the natives. Tourists usually drink whatever they get served.