Right, I forgot all about them sales. I'm definitely gonna have to buy them the next time a sale hits... now the only thing to worry about is which one to buy first. It seems that all the FF games from 3 to 14 (minus 12 and 15's apparently coming to PC soon) are on Steam, so I definitely have a lot of games to choose from in the future...
There seems to be a broad consensus among FF fans that FF6 and FF10-2 were the Gold and Silver Medalists, respectively, for the entire series. If you look online at polls and articles ranking the games from worst to best, you'll find FF6 in the #1 or #2 spots of most lists. FFX-2 doesn't show up as often, mainly because most of the articles which rank the games only rank the main, core games, and exclude the spin-offs and sequels. (FF11 and FF14 are MMORPGs, and also generally excluded from such lists.) But FFX-2 is held in very high regard as well on those lists which do discuss the sequels and spin-offs.
All of the games have things to like, though, and all of them have their fans. FFI is probably the most difficult one for the modern gamer to enjoy because it's pretty damned primitive. But even then it has its own quaint charms.
The Steam version of FF3 is the DS remake from 2006, which updated the graphics and story and gameplay considerably. Having played both the NES original and the DS remake, I can testify that the DS remake of FF3 is not nearly as hair-pullingly frustrating as is the NES original.
My personal fave is FFXII (pronounced "fucksy"), which is in the process of being ported to Windows via Steam, and will probably be released either around Christmas or around the time the latest one (FF15) is released on Steam.