GSM operators?

I want a new GSM operator (the current one is Sonera). Radiolinja (now Elisa) has been tried and found lacking in quality.

Good advice on which operators to try and especially which ones not to try is appreciated. Most of all I don't like surprises. During the Radiolinja times people used to call me from abroad and get no answer; I never got the calls; Radiolinja refused to correct or even acknowledge the problem - they said that the problem must be with the phones abroad, I doubted that so many phones in three countries on two continents suddenly failed in connection with me changing to Radiolinja. Sonera, on the other hand, produced a 131-euro surprise in the bill last fall (which is an excusable offence) and has failed to properly straighten it out so far (which isn't).