I"ve recently been testing 700c wheels vs 26" wheels. The bikes, wheels and tires are different between the two sizes so it's not a true Apples-to-Apples comparison but I think I've gotten a good feel for each size.
My perception is that 26" wheels accelerate faster and make the bike more nimble in tight quarters. They allow wider tires which really smooths out the ride.... a LOT. My perception has been that 26" wheels feel more stable but after riding a 26" Long Haul Trucker with < 40mm tires, I decided that stability was due to the wide tires. The 26" LHT with thinner tires felt twitchy to me.
My perception on 700c wheels is that they hold their momentum better. They are also lighter, which decreases perceived effort for a given speed.
I've ridden 700c wheels exclusively since 1995 and I've decided for my personal riding style, 26" wheels are better. If I was going to do day-long rides I would probably choose 700c wheels.