I have played both. Lumines has better atmosphere and is overall the better experience. However, Polarium is very clever and innovative, and like you said it's unlike pretty much anything I've played before.
They're two totally different experiences, really.
Also don't forget about Mercury and Meteos, both are kick ass.
I've played Lumines, and not Polarium, so I can't make a perfect decision about it.
I've seen both in action and I think Polarium looks a bit more fun, just because of the touch screen. But I haven't played them so I can't make an educated opinion.