It is always going to depend on the photo itself and I do think that smaller prints can draw the viewer in, but I do like a big print. Its great to see all the detail in the image as well as having a bold impact - something a screen never really manages. It is nice to see people step back to take it all in and then lean forward to see the details.
Each to his own though. The worst thing is to see a gallery full of identically sized prints, where no thought has gone into individual presentation and everything looks the same.