I haven't used it myself so I couldn't give you my own opinion, but we do have a few threads here you may want to check out: here
. Maybe someone else will come by with a more recent opinion.
There are other options too: ComicFury
and Smack Jeeves
are the popular ones. A lot of people put their comics up on multiple sites as "mirrors" for more views.
Your tumblr seems to be pretty well set up for a webcomic. I think you'd be fine sticking it out there if you only wanted to use one site. Joining a comic hosting site would put you right in the comic community though, so it's your call. Decide how many sites you'd be willing to maintain for yourself.