It seems, to me, that many people (like me) plump for one (I chose PICs) and then build up knowledge on that (slowly) and haven't got time to compare and contrast to a great degree. It's much like choosing a language (regardless of microcontrollers)... if you want to program something you, quite possibly, will end up choosing a language and then you might end up doing most of your future programming tasks in that language... unless it's totally unsuitable, of course.
For me, I quite like PICs... and I quite like JAL with PICs. There could definitely be more support out there, but there is some, and it's helpful. PICs are cheap, there are many different types, suiting many different requirements and they're pretty cheap. JAL is free... and, although I have done plenty of 8086 assembler in the past, I fancied a higher level language while dipping my toe into this water.
If others have had the time to fully compare and contrast what is out there, outlining pros and cons, then it could be an interesting thread.