Just don't enter the MMO market at all. That's the best
MMO business model!
I'm sure if you leafed through the graveyard of defunct MMO developers, they would agree.
As far as F2P goes, imho as long as the world's economy continues to sputter, and lots of folks have employment, home ownership, college loans, etc. etc. concerns, then yeah, you'll probably have much better luck nickel and diming MMO players to get money out of them long term than getting a flat $179.88 every year out of them, esp. given how often masses of players lose interest in an MMO within 6 months of launch.
F2P in theory gives them a way to even keep disgruntled or "losing interest" player attached to the game, whereas $14.99 a month, generally, doesn't make such players want to stay attached and see how the game evolves. Once that launch happiness is over, it becomes "Do I want to keep throwing $15 a month at this thing?"
I really don't know how F2P is working for the higher profile titles. I know LOTRO, City of Heroes, Champions, Star Trek Online, etc. are surviving or at least doing OK. I don't know if if they're ravingly successful to the point devs are driving Porsches and Ferraris and drinking from a liquid milk chocolate fountain at their desks. If the games are surviving, and they're able to continously churn out content updates, maybe that's all you can ask in today's environment.