A single flute cutter can be stiffer if the grinding design permits.
Resistance to deflection is a good property. Most 2 flute cutters exist
because of dynamics. A single flute OGee, e.g. will blow itself up at
25,000RPM.
Single flute bits have balance problems and are rarely found on cutters
with diameters much than the shank.
http://www.patwarner.com (Routers)