I'm not from Europe, but I have been to many US cons, and can offer my opinion. My personal favorite con is Further Confusion. It has a nice balance of performance, art, and various other things going on that make it worth the trip for me. It is the most expensive con for me to go to every year, yet I feel it is well worth it.
My second favorite would have to be Midwest Furfest. Like FC, they do a nice job with performance, and also attract good artists. Both cons are large, but but large enough to be overwhelming.
That being said, my preference in cons is performance, I am a puppeteer and fursuiter, and I think those two cons offer the most opportunities to perform and to run panels.
Finally, I will be attending my first EF in 2010, and I am very much looking forward to it. I have hear nothing but good about it, as in 2010 I will not be going to any US cons, only EF.
Vixie!