Have run all of these, in anger, in production, at one point or another.
I still have an extremely soft spot for the RAQ2, 64 bit MIPS processor.
Image link - http://dev.gentoo.org/~vapier/pics/mipsel-raq2/inside-main-board.jpg
Nota Bene, NO HEAT-SINKS OF ANY KIND, and yet these puppies could saturate a 10 Mbit connection (of course this was the days before flash and stuff) and the whole mainboard used about 10 watts, most of which was the RAM, the biggest power eater was the IDE HD.
Downside was it was MIPS, which is a lot like the downside of the Acorn ARM based A series and Risc-PC series, eg not x86 compatible, ergo not mainstream.
Now that ARM is used is zillions of other devices, ARM is no longer the backwoods, everywhere except in "a computer" eg desktop or server.
Which means ARM on the desktop or ARM on the server won't suffer so badly for not being x86... it will still suffer, but not so badly.
RAQ3 went away from MIPS to x86, IMHO because of this accessibility and availability of x86 code, not because it was technically superior to MIPS... one RAQ3 wasn't more powerful than two RAQ2 in any sense except power consumption and thermal rejection.
In practical terms x86 has gone nearly as far as it can go, both in terms of light speed and die size, and thermal dissipation per cubic mm, so the alternatives are catching up, not so much because of sheer lifting power, but because of thermal dissipation per cubic mm they still have "development room" left to play around in.
The next 5 years or so are going to be interesting, as this "development room" is explored and used up, and especially so if anyone comes out with a robust cross architecture compiler / translator.