I really don't know about photobucket but with tinypic you have to choose the size of the picture to be uploaded. There are a couple different options ranging from original to thumbnail if I remember correctly. Maybe photobucket has changed their default upload setting.
Go with Flickr. They have no ads, easy to use, and you can edit your pics with some neat software.
Been using them for a couple of years now, never had an issue. Plus they just revamped the site, and made it a whole lot nicer.