I do hate these open ended this vs. that vs. this vs. that threads
But here goes:
Utopias are pretty good bass wise and a close performer to the Seas (I'm assuming G18 since you don't specify) but the Dyns and Hex are much worse, with limited output.
Midrange wise, I enjoy the sound of the Utopias. It's pretty smooth, a bit heavy, and liquid sounding. Hex sound mushy and muddy to me (the old Eton series), and the Dyns being probably the most detailed out of the three, but a bit laid back. Seas would really depend on the model.
As 10k2hvn mentioned, these all sound completely different. It may help if you narrow down the type of driver you're looking for.