Once, I tried a quite unkown digital servo, named Keil. It was reasonably priced and had good specs. It worked well, but when I upgraded to a KO radio, I got a lot of glitching. After a lot of experimentation, it was clear that the Keil didnt worked with all radios
The moral is: definately go with a wellknown and reliable brand.
Personally, I went with the KO PDS 2123, and it have served me very well for around 3 years. But Futaba, Airtronics etc. might be as good as well.