I'm a pretty biased GEO fan, but I have used his skimmers and reactors for a while. I don't have personal experience with the Schuran, but have read about how horrible they are to tune, not to mention if you need parts for them....the main company is in Germany and if you need something now, you will not get it.
As for Deltec, definitely a quality product with a big price tag. People seem very happy with them and I think they buy the brand for that reputation of being the best, but they are also paying for it.
The GEO line is here in the United States, owned and operated by George out of Ohio...he is a stand up guy who will be here for years to come and his products are very reliable...in particular, his reactors are truly set and forget.