I will add that if you have a full table of 1st level PCs with a slant towards martial classes, (i.e. 6-7) MotFF is not the death inducing meat grinder that it can be with just 4. I ran it as a first quest for a full group including a Bard, Summoner, Samurai, Fighter, Ranger, Sorcerer, and Cleric and they more or less owned it up until the end, though no players died. It really comes down to whether or not the players want a dungeon crawl or a series of somewhat diverse encounters nested inside of a fetch quest. Since my group wanted to carve lots of things in to tiny pieces we opted for the MotFF instead of Intro 1.
I PFS because I don't need to have a consistent group to play. I am married with 3 small children and we have enough difficulty juggling our own internal schedules without having to include those of a regular gaming group. With PFS, I can find a game in jump in as I am able or, as I am doing for the 1st time, this Sunday, posting an event and running it.