Originally Posted by badger1

Taking your question head on, that is assuming a 'hybrid/mtb' riding position,and assuming that you equalize the gearing, roughly same speed for the same effort. One of the best discussions of this I've seen is by Andy Blance on the Thorn (UK) website: yes, 700c has a slight advantage in rolling resistance over 'bumps' BUT 26" with, say, wider 1.5 tires at lower pressure have less rolling resistance over ever-present small road surface imperfections -- probably pretty much balances out. 700c 'wins' at sustained, 'racing' speeds due to aerodynamic advantages and other factors (e.g. narrow tires at high pressures), 26" at more usual touring/fast touring speeds due to comfort (wider tire, lower pressure), relative wheel strength, and (importantly) ability to accelerate slightly more quickly. As others have said, figure out your priorities, best fit, and choose accordingly.