Sure. I'm going to simplify things just because of space constraints, but I'll highlight what I think are the biggest differences.
- browsershots.org: Free option (go to the back of the line), paid option (priority), but ultimately screenshots only.
- Adobe Browserlab: Pricing not defined? It will be pay, but I don't think they've announced pricing. Single page only results. Just does screenshot comparisons.
- Litmus App: I'm not sure if they're completely out of the space. They've been focusing on email render testing. Single page only results, but pretty slick UI.
- browsera: Does some of the cross-browser issue detection (we'll be adding this soon, but it's not there yet), but feels clunky to use. Limited browser selection, but they said they're working on that. Doesn't do the general site issue detection we do.
Sorry if that was an oversimplification. I'm not trying to misrepresent what the others are doing. Some do some things better than us now, but we're moving pretty quickly on our product, which we think is better in other ways. Primarily, we're amongst the fastest and easiest to set up & use.