This is a frequent question. The best options are a Pulsar Apex XD50a 2x 384 resolution, 50 hz, 25 micron unit or an Armasight Zeus 336 (resolution) 3x 42mm 17 micron 30 hz (or 60 hz, depending on which you buy).
The Pulsar has some really neat firmware features such as Picture in Picture zoom and some nice reticle selections and colors that can be customized. It has nifty controls such that once set up, the stuff you really need is easy to access. The down size is the 2x native magnification.
The Armasight is more solidly built, has a 3x native magnification, and is more compact.
The differences in resolution are offset, I think, but the difference in micron distances between sensor pixels such that they both look good. The Pulsar has a surprisingly good picture despite having the larger micron gap. It makes up for this with the larger lens and higher resolution. The Armasight has greater magnification.
In terms of hz or refresh rate of the image, 30 works fine. The 50 of the Pulsar certainly provides a smooth image. You can go with the 60 on the Armasight, but I don't know that it is necessary.
Give Clifford a call at Third Coast Thermal 832-827-4574 and he can tell you more.