Quoted:
You can kill a shit ton of hogs with a good gen 3 740/760 or clip on unit. Does one work better than the other?  That depends on conditions. If your hog hunting black really stands out using I2. With a good tube you can hunt the darkest nights without a illuminator and still have good range. Open areas like pastures are much better than river bottoms. Nights with a little moon or more you can see clear as day, and have great id on targets. Rain, fog can be a issue and give you limited range, and have issues with lens fogging.  

Now Thermal is far superior in detection over I2. In the past proper id was a hinderance due to lack of resolution. While still not on par with I2 a 640 core is dam good to ID a animal. Like someone previously mentioned the more you use thermal the easier it will become to ID a animal due to the way the animal moves. Thermal can still have problems in certain conditions. Take a relatively cool overcast day that is windy and you will be looking at a washed out image in your viewer.  Also, on nights were a front comes through and you have a wind chill effect your image will degrade over the course of he night.

Navigation I2 can't be beat. A pvs or dual set up with a thermal viewer paired with a quality gen 3 scope is pretty hard to beat for hog hunting.