The simple answer is to get both if you're serious and have the budget. However if your budget can only afford one...go thermal. There is absolutely no contest in detection and recognition.
I used NV for over 20 years in the Corps, and while a PVS-14 (or better) is superror for movement ... especially in unfamiliar terrain... there is no way that you are picking up critters at 1K plus yards with them, or quickly ID'ing specific animals on the move in shadows etc...
As a rancher, I only need thermal on my land. I know where the holes are. However as a hog hunter on my friend's properties, I have actually walked face-first into a barb-wire fence while putting a stalk on a boar in a no-illumination situation. Not my finest moment, but I killed his problem hog a few minutes later.
To argue with a perspective mentioned above, a decent 320 unit will allow you to identify the difference between deer, hog, cow, coyote, and calf at a solid 500 yards or better. It might take a little practice, but the first time you're out hunting EVERYTHING looks like a hog. I have an 1100 yard and 800 yard pasture, and I have no problem figuring out what I'm looking at as I enter them. THE BIGGEST problem is identifying a lone boar that is near a group of young calves, but it is not hard within 250 yards.
That keeps initial cost to between $3-4K.
Good luck.