Charge shots are extremely situational and you should really go by what you want out of the normal shots.
that being said, I like my Polaris a lot better than I liked my Cryotech Mk II (I started liking it more when I made it into a Kilowatt already). The normal bullets do so much more damage and the knockback from any direction allows you to shape mobs into the clump sizes that you want, or scatter them if they're too bunched.
I like the Kilowatt Pulsar series a lot better, personally.
Can someone post a hail driver charge shot video? I'm debating on whether to keep my cryo, or switch to pulsar. Thanks xP