Any planet eclipse gun for the money is a safe bet as parts are readily available and majority of events will have a tech available if anything does go wrong.
On the other hand, Invert Mini's can be very cheap to pick up and are very robust. I have had my mini for almost 3 years and the biggest issue I had was on O-Ring on the gas exchange which the spares kit had in it anyway.
If you get offered a Vanguard Creed/Demon, i personally would not touch it. I have one as a backup at the moment and when it works is one of the most incredible markers i have ever shot. However it does tend to be quite temperamental and requires alot of TLC.