I'm saying Super Mario RPG size, but I confused that with "same size as Mario" (since I was thinking about their sprites... looked similar in my mind), so I essentially messed up my vote. Meant to vote "slightly bigger than Mario". Confirmed that when looking up videos of Bowser from Paper Mario versus Super Paper Mario. In the N64 one, Bowser's like three times Mario's size, and that was odd. In the GameCube one, he's a little less than twice Mario's size. Yet the Bowsers in both those Paper Mario games are probably the same sprite. So either the Mario sprite got a makeover and was made bigger, or Bowser was made smaller.
As for the general look of Bowser (which wasn't mentioned, but I'll do it anyway), I prefer a clean look but slightly rugged (visible bumps but not bumps everywhere), not so cutesy as to be bubbly, not as realistic as the Smash Bros. games (by the way, I think Bowser in Smash Bros. Melee looks terrible in the static render, but wonderful in motion), slight orange hue instead of golden colors.