Which is more profitable – an MMO with a monthly subscription or a free-to-play game?

Although, as I see it, there's a reason why LotRO switched from a standard subscription model to a free-to-play one. So, it seems that everything depends on the game's popularity. I also wanted to add something about the target audience, but I doubt it's too diverse. Marketing isn't such a primitive thing.
And, Revan, I hope you'll forgive me for a little bit of moderator overreach. The thing is, I was bribed and forced to abuse some of my official powers.