That's a very good question... At first I thought FE7 ruled and all because I only heard of FE7 and FE8 and my friend didn't like FE8. But then I played FE9... It was so much cooler for some reason. The characters, no annoying promotion items, no arena (I hate it when people win a game just because of the arena) and the plot was so interesting. I do miss the tactitian but you never decided anything. In FE9, you could change the storyline a bit (not really but they give you options XD). The I played FE8, the game was just as fun as FE7. I sometimes preferred FE8 but now it's more of a tie. FE6... I didn't like it that much but it was continuing FE7 so I wanted to play. And last week thanks to Sir Canas I found a translated version of Gaiden. But I don't like it that much because I like FE games a lot for there plot... But there is practically no plot to it. I didn't get far at all so maybe there's a plot later on. So my list is like this
FE9-10
FE7-8
FE6
FE2
(yes I know it looks like I'm putting them in order)