I bought a Virus TI Snow 3 years ago. I loved it so much I sold it after 10 months and bought a used Virus TI Polar to replace it.
The first difference is that the Snow only has a few knobs and no keys of course. So I wanted the Polar for that "hands-on" factor b/c with the Snow you have to use the TI software due to the lack of knobs/buttons.
The other difference is that the Snow, being the smallest model, had the lowest hardware specs like the Snow had half the RAM the Polar does iirc. That means the other non-Snow models have more multitimbrality so you can use more parts. The Snow is multitimbral with 4 parts iirc but it can run out of polyphony with less parts depending how complex your patches are, how much fx they use, etc.
The TI2 has 25% faster processor and more polyphony than the TI line. Hope this helps.
I still have my Polar, it's my desert island synth bc of its versatility. Watch Virus TI training video courses and really learn your way around this instrument. Most people who own one get caught up with just using patches, since there are so many soundsets available. But since they never really dedicate time to learning it, they never realize how deep this synth is.