I cannot compare as I am not a FB user.
However, out of all the forums I have used (owning different cars along the way), this forum is by far the best one to use. I use it daily and it has been a great base of knowledge for me (I virtually knew nothing about the MK5 before purchase), but feel like a little expert now, armed with knowledge gathered from this forum. It has even encouraged me to start doing the odd little job on the car here and there.
FB does not seem like my cup of tea. I will continue to use civilised/mature platforms, such as this forum and others like it.
I do not have a problem with people using FB, as long as they can gain what they require from it. If you find it childish/annoying, then move away/do not correspond. I'm sure there will be areas of it which will be useful, i.e. someone mentioned 'bargains to be had'.
Whatever platform you utilise, keep smiling and enjoy the GTI..........