I mirror on Tumblr, but otherwise I post on my main website. I get more readers on Tapastic, but grassbladescomic.com looks neater on my business card than tapastic.com/Grassblades. Also, I haven't gotten any ads for it yet, though I'm thinking about looking into it as soon as I'm less busy (whenever that will be =.=;)
I used to use smackjeeves, but that was years ago, so I don't know what it's like these days. It was decent when I used it, but that might have changed.
Before that, I also used Drunk Duck, which I do NOT recommend to anyone - though I don't even know if it's still around. It had major issues, an entirely terrible design, bad forums, and also tended to implode on a regular basis. The one thing it did teach me was the value of mirroring my work on several websites, in case something goes wrong.