LOL, It's true that a calm large breed dog takes up less space than a hyperactive small/medium dog. You get accustommed to stepping over a big dog, you never get accustommed to having a 'zooming' dog run into you and scream like he's just been lit on fire. (Hmm, do ya think I've had that happen to me before?)
ENGLISH mastiffs are the calmest of the mastiffs, I believe. Neo's run a close second. (Neutered males, or females. Unaltered males are an incredibly large, slobbery handful)
My prob. with the English Bulldogs is that, sweet as they are, they come with so many health problems and a lot of people don't have $1800+ to spend on buying one from a responsible breeder. (Don't ever get the cheapest one you can find, you're likely to wind up with one messed-up Bulldog)
Mastiffs that AREN'T calm include the Dogue de Bordeaux--Looks like a big marshmallow, but for the first few years is quite the hyper bundle of joy. (115lbs of it, to be precise) The Bullmastiff -- Again, very hyper puppyhood.
One breed I certainly don't recommend as a calm breed is a Papillon. Amusing, yes. Calm, no.