Are you looking for regular or thermal? Intended purpose? Environment it'll primarily be used in?
Most important: How much are you willing to spend (diesels are expensive these days!LOL)?
There are numerous options, but they'll vary a good bit in their suitability depending on what you want them to be able to do for you.
Example 1.) A PVS-14 is an excellent general purpose choice, particularly if you are only going to buy one device. It'll allow general navigation, decent engagement when used with an IR laser, and can be coupled on the rear of daytime optics (sub-optimal choice but it can bridge the gap). It's a good all arounder but it won't make a pig (or other game) jump out at you like a thermal will.
Example 2.) A thermal sight will make game and other heat signatures leap out at you, but they are somewhat lacking for purposes of general navigation and target ID (unless you are fairly close)
Example 3.) A dedicated weapon sight will be superior to a PVS-14 for target engagement at distance, but you won't like trying to use it for anything else, as you end up with your head glued to your weapon.