We've owned a few for work and demo'd a few for play. My advice is to test drive multiple brands and buy what you like plus an extended warranty. Reliability is good across major brands, but the machines aren't indestructible. Our service tech relative works on the brands mentioned thus far plus three others. He says the majority of problems aren't from quality, but rather from lack of maintenance, DIY maintenance gone wrong, and wrecks/misuse.
He has some pretty interesting stories. It turns out side by sides aren't submarines or hovercraft, and using them as such is very expensive. And, if one is too drunk to drive a pickup, taking the side by side instead is a terrible idea.