Wow, tough question to answer. Up to now, the Type X's have been, hands-down, the over-all leader in anything I had previously experienced personally, with the possible exception to a pair of JL W7's (but, they weren't sealed and were peaking where I'd like sub-bass to be flatter, and weren't as musical as the Type X's).
I can't say one is really "better than the other" because they are distinctively different. The Type X have the "shake the hell out of your vehicle" factor. They also seem to be more at-home in the absolute lowest of audible frequencies. The Type X also have better sound quality than anything I've heard to date, other than the RL-P's. The RL-P's are more responsive and snappy. The RL-P's also seem to be able to hit higher SPL with average music, and almost half the power.
It's almost a case of having a set of both. One, for primarily uber-deep bass songs, and the other for good ol' punk rawk, classical, and everything in-between.
Now, keep in mind that someone can "shape" their response significantly through enclosure type and tuning and maybe a bit of EQ. I'm just talking about generic sealed enclosure performance in my vehicle.
The enclosure is the same for both pairs of woofers, and so is the amp, but the power is different. It is 1.35 cu. ft. per side, sealed, and dampened on the internal walls. Power to the Alpine Type X's was around 1000 RMS each, and the RL-P's are getting around 500-650 W RMS each, at max.