If you buy, sell, and trade machines frequently, I would stick with used machines due to the NIB hit. If you are going to buy it and keep it forever, get a new one if that is what you want. The biggest downside to buying brand new machine that you will keep forever, is the lack of code on some of the new machines. There is a Deadpool LE at the company office that has .86 code on it because no-one has the keys to the backbox to change it. There is a Deadpool Pro at the local arcade with the latest code. The Pro with the latest code is much more fun than the LE with the more basic code.
The way to waste the most money on pinball while having the least fun is to always buy the latest, and sell/trade the second latest before the code has time to mature. If pinball machines don't stay in your house long try and stay at least a year behind the latest release if you want to have the best experience.
With that said, mine are all 90s Bally Williams!