Of all the ones that I've personally heard, the MCP600 is.
Have heard:
Johnson CM30-P7
Johnson CO30-P5
Davies-Craig EBP
Swiftech MCP600 (also available at
www.cooltechnica.com badged as AquaXtreme 50Z-DC12)
Swiftech MCP650
Laing D4 (effectively an unmuffled MCP650)
Both the Johnson pumps are not recommended due to very lower motor MTBF due to the use of brushed motors.
Will have the March 893-09 in my hand soon.