I have comapred both ASM and euroreef. I personally use a EuroReef that I purchased used for pretty cheap.
There is a noticable difference in build construction between the two brands. The euroreef seems much sturdier in contruction than the ASM, however, they both perform virtually identical.
IMO with both thse skimmer you are really paying for the needlewheel pump, because to tell the truth, I'm not really all the impressed with what you get from euroreef for what you pay. You get an acrylic tube with two pipes connected to it and a union valve to remove the skimmer cup.
Pretty friggin simple. Compared to something like an MRC, a euroreef seems pretty cheap in quality (just my opinion). Of course with any beckett style skimmer you have to purchase a good pressure rated pump, so they do end up costing more most of the time.
BTW, you may want to check out geosreef skimmers, virtually identical to euroreef, but I would suspect much better construction...
Mike