I'm surprised at these comments here on PPRuNe. The comfort of an aircraft is little to do with the airframe type and everything to do with how the operator has set out the seats in terms of pitch and such like. The airframe just gives an airline an empty shell to play with.
There are some marginal issues, such as the A320 fuselage is 6" wider than the B737/757 fuselage, which gives just a fraction of extra room to everyone as you can only rig either of them up 6-across. Some operators don't even do this - Northwest for example puts the same seats in their A320 as in their B757, with just a wider aisle, in a triumph of spares holding costs over customer comfort.