I have, and love, my Bernina. I had, and hated, a Riccar.
My advice is to TRY THEM OUT! Our local Bernina dealer will set up a machine for you and let you bring your own fabric to try out. Look at threading - some are fiendishly difficult, others are easier. Look at quality makes such as Bernina, Husqvarna, Juki, Brother - all these manufacturers make industrial/commercial overlocker machines, and the technology is available in the domestic market machines too.
Make sure that you get a machine that has 4 threads, but that will also overlock using three. A three-thread machine can get frustrating. Ask the dealer if they run taster sessions or post sales training - you can only learn so much from a DVD or instruction book. You can learn so much more by watching, and asking questions of, another user.
As with everything, buy the best you can afford. Make sure it has a guarantee and aftersales care. Then take it home, play and enjoy!