Playtech software is generally nice. So is MG, so is Crypto, RTG has some good games too - depends on the games you like. I think the main concern would be overall reputation of the operators on each platform as you will invariably get lumped in with "Playtech" operators or "RTG operators" or "MG operators" as a whole. So although its not strictly the question you asked, i'd advise researching reputations aswell
Software is obviously important, but it doesn't matter what software you are on if you can't build a solid reputation as an operator.
My personal software choice is MG, but I'm not adverse to a bit of Crypto video poker and Boss and Playtech certainly look the part even if the games aren't quite s exciting as MG on the whole.
Cheers
Simmo!