Asking what Linux distro is the best is like asking which chips are the best. Your answers are not limited to just the ones you know about. For you its going to come down to which one you feel most comfortable with. I started playing with Linux years ago but didn't become a serious user until about 6 years ago. I wish I knew more than I did and am thankful to know what I do. The best way to learn for me is to jump in and start doing. Some can't do that they need books and other things to help. Some wan't friends to assist and help. I depend on the forums and my own knowledge. I know your an intelligent person and can figure things out fairly well. I have seen many of your post after all and feel fairly confident in that statement.
My Suggestion is to first learn the linux way. I am personally a fan of Fedora but its not really a starting point. I would say Mageia (A Fork from the now defunct Mandriva) or stay with Ubuntu. As far as your desktop environment I would try them all and see what feels good. (Gotta Love the Live CD for that) I recommend using a usb drive for your distro and just get comfortable using it. Start switching some of your programs to cross platform stuff like VLC instead of Windows media player, Chrome or Firefox instead of IE. No real substitute for Excel so if thats something you do often then keep windows around for that kind of stuff until you feel you no longer need them or have found comparable alternatives for your needs. When things get difficult remember your friends We'll help as much as we can or at least point you to the right direction