though I choose the portrait, I think that only depends on the feeling that you wanna create unto the image.
portrait is very personal, a bit like a two way conversation between the viewer and the photo, but landscape looks a bit more impersonal but more like its the photo speaking for itself, it's like a monologue but an interesting one. and square is very restrictive but it has a naughty feeling of being the peeping tom ( heh, I always thought that about the square format)
but it all depends of the image, so choose the formats that will fit the character.
Each has it's advantages, but landscape and square might give you more negative space to play with for the text you include in the comment section. Mentally I find it more difficult to work with the rule of thirds in a portrait setting, but it's nice to be surprised.
I voted... but I'm still torn between square and landscape.
(and yes, this lurker finally sees the sunlight. CAPSLOCK!!!!)