Deltas: there are fast overall, but not allow a direct extruder, retractions problems, very difficult to configure.
hbot: need a very rigid structure and robust linear movements or else the print will be deformed.
corexy: almost no flaws, the only i can indicate is the length of the belts if you build a big printer.
I have before a prusa steel model and now i have an corexy printer. The corexy beats the prusa in speed, print quality and reliability by miles.
Your mpcnc use a very similar mechanism of a ultimaker. Is an design that prove is possible to build a good cnc with cheap hardware, but i think is main success was because you have chose a great mechanical design at first.
My corexy is a dual direct mk8 extruder (carriage of 800gr) and allow me to print without any artifact up to 80mm/s.
If you have some time check some corexy printers, i think there are the best mechanical design you can chose.
a link of my printer: http://www.thingiverse.com/thing:1003119