I have a Blichmann Riptide. Very nicely done, long cord, on-off switch on the pump, splash-resistant, quiet, includes a control valve, easy to take apart and clean as needed. But it's $200, so you pay for the features and engineering, which are terrific.
I recently got a couple MK II pumps as part of a package purchase from someone going out of brewing. They are as quiet as the Riptide, which surprised me. They are rated at 5 gpm whereas the Riptide can move 7 gpm.
The downsides to the MK II pumps are these: the cord is shorter (5 feet vs 10 feet for the Riptide), no on-off switch, no valve to control output. The cheaper MKII has a plastic head; of the two I have, one had the plastic head, one the stainless one. The threads on the plastic head had been cross-threaded which meant an operation on it. I eventually just replaced the plastic head with the stainless head.
The Riptide, theoretically, can orient the head in any direction, whereas the head on the MKII has only 6 positions, 60-degrees apart.
The MKII is smaller, which in some contexts is nice.
Price-wise, the MKII is $100 with the stainless head, $70 w/ the plastic one. Then you'll need to add a ball valve or some such to the output side to control flow, that'll be, what, $15-30? So it's significantly cheaper than the RipTide.
I had intended to sell off the MKII pumps included with the stuff I bought, but now I'm not planning on doing that. I can see applications for extra pumps, and I intend to use them for that.