From what I've read, variables are no more prone to failure than fixed. While any scope can fail I think if you get a good scope your odds are in your favour. Personally I've found Leupolds tend to be more reliable, especially on a heavy recoiling rifles. (I know I'll get a lot of "hate mail" over this but I've actually been there when several scopes wearing names like Trashco and Bushsmell have failed or performed poorly). I have had a Leupold fail on me but that was after over 10,000 rounds down the tube, and they had it back to me, free of charge, in less than 2 weeks. (Yes that's correct, well over 10,000 rounds before any problems).