Which cell phone operator?

I spent 3 month abroad, but I didn't switch to a local mobile operator. Why? Is it loyalty to my national operator? Hmm, I don't think so. No time, no need, no motivation, in fact. But the problem also is that it's sooo difficult to choose what you don't know the real situation on the market to judge. Well, I will try to get more information and will have finaly a new number :) in the next year...