I have a feeling Firefox OS is going to be big. from what I've seen of YouTube demos the OS is quite responsive on modest hardware (gs2 and nexus s). I've had no luck this week trying to build the OS for a gs2. I'm hopeful that I'll have more success compiling for a nexus s.
Firefox OS is great so far, it has its quirks but its still very early days. There is no question in my mind that it will be a serious contender. There are so many devs out there who just want to code for one platform (web) and cant be bothered to go native (ask anyone using phonegap or sencha)...so a giant influx of good apps is not far off. And best of all, its built to open standards with no walled garden.