I can easily say this is the hardest part of making the final decision to become a Linux user, especially full time. There are so many distributions out there and many of them offer more benefits than anything. I definitely say to continue testing and check out Distro Watch - it is a valuable site to find a plethora of distributions. Plus, it allows you to see just how up-to-date distributions. When I become interested in a distro that was not familiar to me, I try to check it out on Distro Watch to see if it is still updating in any way, which is very important. The decision can be hard to make and you might even become a distro hopper - I can admit that I have been guilty of it at times, haha. Good luck!
Yeah, that's the hardest part. The decision can be made on interest and what kind of packages and applications would you been needing to run. I choose Ubuntu at first just cause i was introduced to it first, but now i have plans to make my move to Linux Mint. I prefered the old Desktop Environment, i'll probably wait till Unity stars to look simpler, or maybe it might not.