I think of it like this: the more armor you must acquire, the more fun it'll be, so I'd go with the latter part of the 14th Century. For me, anyways, a lot of the fun is in the building of a kit, you know?
Thing is, if you have a good base to start with (a good mail coat, or some good plate armor parts) then your kit will be that much better when you're finished putting it all together. I've noticed that I've slowly made my way toward more current times (my first kit was 11th C, all mail, butted at that- still have the coif!) as I become more enamored with plate armor and the myriad styles and designs that you can get ahold of makes it quite a fun and rewarding exercise.
For next year, I need new legs, a helm and I need to tailor my hauberk to fit me better; seeing some of the rigs you guys wear has gotten me to thinking.
