What do you mean by "most supported"? Almost every vendor offers a $30 to $80 retail boxed version which includes a good sized manual and limted phone support. For more money, you can get more phone support.
In general, though, there are literally TONS and TONS of people, websites, newsgroups, BBSes and LUG (Linux User Groups) who will be glad to help you. I kid you not, 95% of my linux problems I have fixed by surfing the web looking for answers, the other 5% I had to mail somebody or post a question.
Linux.org has links to the 100+ "Howtos", which is a great place to get started.
[shameless plug] I like Slackware. If you're comming from FreeBSD (good for you!), Slackware is what you may be most comfortable with. It's most like 'old' Unix (aka System V). My roomate switched from Slackware to FreeBSD with minimal issues. [/shameless plug]