I like Panoramio because they prefer large images. If it is scenic (and not three guys getting drunk on the beach) they also link to them to Google and Google Earth. (Google not surprisingly now owns Panoramio)

If it is something I am going to put up on various forums, I use tinypic.com. The drawback there is they don't have a good management system for your photos. So, I tag them with relevant tags and keep a log of the tiny urls to my pics.

Photobucket and pbase are okay if you like those interfaces. I don't. With over 25,000 online images, I prefer something I can manage. (my own database)