Which operator is the best? What are the prices?
I use T-Mobile (formerly ERA), and I am satisfied about their network and service. They're prolly not the cheapest, tho.
Play is cheaper, but their network coverage is worse. I have some friends using Play, and they have no signal in some places, including their rooms/flats...so sometimes they need to lean out of the window/get onto the balcony to have a conversation. Especially fun in the winter with -15C! :))
Orange is a bit better, so I've heard, but their service seems to be lacking.
The prices: best to check yourself on the websites, that should be easy to find out.