What df2x4 said. I personally run those Kappas and love them.
After looking at the Kickers, I wouldn't recommend those to anyone. They've got a sensitivity rating of only 88dB, which is terrible. On the other hand, the Kappas are 94dB. This is really one of the most important specs IMO. The higher the sensitivity, the louder the speaker will play and less power is needed to drive them into ear bleed levels. With amplifiers, you don't end up with a linear reward based on power. Ie, 100 watts won't net you 10 times the level of a 10 watt amplifier. Its more like an extra 6 dB of output, 100 watts vs 10. That's why sensitivity is very important, especially in a car. It's also why that spec is pretty hard to find for a given speaker.
