So, the bravery system is the subject of heated debate. Here's a proposal that I think both premium and VIP will find agreeable.
Let's have F2P opening just normal, premium hard, and VIP elite. Thus far this has been said before. But I would go further:
As a 3500 favor reward (maybe with a pricey store purchase option, just like favored soul or any other favor rewards), you move one step up in the table. F2P with 3500 favor (really tough to achieve but possible) get to open hard, premium would be able to open elite, and what about VIPs?
VIPs with 3500 favor get to open epics at lvl 18 (1st TR) or 16 (2nd or further TRs).
Please try to be constructive on your criticism.