Why does the trial have to be 14 days? It sounds like you can get the value from your product in 7 days, perhaps less. Free trials are the period you have to convince them to hand over their cash, if that happens within the first minutes of using the software - get it then!

I would not advise offering a free version, they will be a drain on your support resources and you'll end up hating them. Or at least, I did :) - it is a lot easier to deal with an annoying user knowing they are paying your bills.