Ah, yes. This poll. Coming from a forum where polls are completely anonymous, I did not hesitate to choose a silly answer that was an obvious exaggeration of my true feelings. However, I see things are a little... different here, and you can see who voted what. Now, everyone can see that I voted "Rock Raiders, duh, Power Miners suck", which is a laughably immature answer that I chose only because I thought it was silly and I would be anonymous. Since I'm not anonymous, I do feel it is necessary to explain that my true feelings towards Power Miners aren't so immature.
Instead, I feel that, design-wise, the Power Miners sets are much better than Rock Raiders. Yes, I prefer the sci-fi futuristic style of Rock Raiders, but as a LEGO fan, I cannot ignore the fact that Rock Raiders sets consist primarily of big, chunky, specialized pieces that do not leave much room for a truly engaging building experience... in other words, Rock Raiders is "juniorized". Power Miners, on the other hand, was released ten years later, and it definitely shows. Compare the build of, say, the Chrome Crusher to the Thunder Driller; the Chrome Crusher is basically cockpit, rollcage, drill, laser, four wheels, and some other bricks slapped on a chassis, whereas the Thunder Driller uses much more versatile LEGO elements and even includes gear functions. While, again, I prefer the color scheme of Rock Raiders, Power Miners uses its colors in a much more streamlined fashion while Rock Raiders seemed to almost haphazardly throw in tons of different colors. Power Miners has other things I like as well. Multiple sizes of Rock Monsters (ranging from Rock Goblins to Crystal Kings), Lava Monsters, Energy Crystals of all colors... things that would appeal to a Rock Raiders fan such as myself.
But, at the end of the day, I still prefer Rock Raiders. As mentioned before, I enjoy the more futuristic designs of Rock Raiders vehicles, and the grey and teal color scheme looks much cooler in my opinion than the lime and orange color scheme of Power Miners. I also find that the characters in Power Miners are far less memorable than those of Rock Raiders; while they were given bios on the official website, they always seemed generic and interchangeable in comics and other media. The goofy depiction of the Rock Goblins (toilet humor and all) did not appeal to me, and while their concept art looks awesome (seriously, that concept art resembles the mental image I had when first hearing that Power Miners Rock Monsters would be a blend of rock and crystal), there was something about the physical appearances of Rock Trolls in the final products that made them look just plain odd to me. Personally, I also prefer the Rock Raiders storyline over that of the Power Miners; while "stopping Rock Monsters from creating earthquakes and destroying the planet" should have been engaging, I think the combination of unmemorable characters and goofy antagonists made it hard to feel like there was anything to invest yourself in. And, of course, there's the Rock Raiders PC game, the very game that this forum is founded on, and Power Miners had no contender with that.
So, at the end of the day, even though I acknowledge that Power Miners has far superior set designs and is a decent theme in its own right, I'll still personally prefer Rock Raiders. However, Power Miners does not "suck", and if you prefer Power Miners, I'm happy for you. Much of the above paragraph, after all, is based upon my mere opinions rather than actual hard facts. It's just my opinion, and my opinion is that Rock Raiders is better than Power Miners.