Conventional 700c hybrid wheels are approximately 28" in diameter. Smaller 26" wheels are ideal on bikes with smaller frame sizes because they allow the bike to be better proportioned for riders below about 5'6" tall, where a larger wheel would mean that the front of the bike had to be positioned too high and too far from the saddle for comfort simply to make room for the wheel. So on all our models with frame sizes below 17" we exclusively use 26" wheels.
But smaller wheels also have other advantages. They are a little lighter, not only making the bike slightly lighter overall, but also meaning it accelerates more quickly and feels slightly more nimble or responsive to ride. They are also inherently stronger, so for heavier or taller riders they can provide an advantage too.
Are there any disadvantages?
In theory a smaller wheel rolls less well on rough terrain (i.e. the same size of bump in the road surface will stop a tiny wheel, where a huge wheel would roll over it). However in reality the difference in size between a 26" and 28" wheel so insignificant it would be almost impossible to notice - the choice of tyre, and pressure it is inflated to, makes much more of a difference.
Another difference between the wheel sizes is that they will slightly effect the gearing - a bike with small wheels effectively has slightly lower gears than a bike with larger wheels. This can be an advantage for the steepest uphill slope, where a very low gear is a good thing. It could be a disadvantage for the fastest downhills, but in practice all Bristol Bicycles have more than enough of a gear range to cope with this - on a bike with smaller wheels you simply select the appropriate gear without thinking about it, and don't even notice the wheel size.
In summary, smaller wheels have several advantages without any real disadvantages. Bristol Bicycles with larger 700c hybrid wheels are available in the larger frame sizes for those who prefer large wheels (the Park Street model). The models with smaller 26" wheels, but otherwise identical components (Stokes Croft and Whiteladies models) are available in a full range of frame sizes from XS to XL. So you can take your pick.