If you're in the market for a thermal be sure to look into a companies warranty. Although a lot of them are going to five year warranties which is great, seems to be the new norm. These thermals aren't any different from other electronics, something is bound to go wrong with them eventually with enough use.
I've had a Bering Optics for three years now and haven't had any major issues with it. My hunting partner has a Pulsar unit and his has been problem free as well.
Also don't forget who you're buying from. Your dealer can be a major help in getting you into a unit that suits your needs; and going to bat for you if you have any issues/warranty work.