For tracking wounded game and in the lower price end, it's going to be the FLIR Scout TK or the Leupold LTO Tracker. There are tons of opinions and reviews on both out there.
I sell both units mentioned above but I'm partial to the LTO Tracker for 3 reasons. It has a thermal core sensor resolution of 206 x 156 vs the 160 ◊ 120 of the TK. It has a a 30Hz refresh rate vs the 9Hz refresh rate of the TK and last but definitely not least, is the fact the LTO Tracker has a very long battery life running on 1 CR123A battery, where as the TK has an internal battery that must be taken to a power source to be re-charged.
If you move up from there in to the next price range, you would be looking at something like the Pulsar Quantum Lite XQ23V for $1,699 and it is in a WHOLE other ball game from something like one of these sub-$1,000 units.
Night Vision, Thermal & Accessories
Pulsar, Sightmark, FLIR, Armasight, ATN & More