What image services do you use to post to social media?

Posterous-_1__medium Square_logo_medium    Twitpic-logo_medium  Mobypicture2_medium

I can never seem to decide and keep bouncing between Posterous and mobypicture.

With so many image/blogging services to choose from to host your images, what is your favorite and why? 

Also, when you use your choice of twitter client on any platform, what is your default?