I like BBW Cupid. It's the most dedicated site I've found for plus-size singles interested in serious dating. I really liked that I could be upfront about being a BBW and it was celebrated, not just tolerated. The crowd is also really friendly and body-positive.
Best of all, the men on there are specifically looking to date plus-size women, so you avoid a lot of the rude comments you might get elsewhere. The big con is that it's not free to message people, but in a way, that keeps out the time-wasters.
So, I'd say it's definitely worth creating a free profile just to look around and see the vibe.