[quote name='Indignate']What's the one that isn't the best of them all? I'd rather start with that one and build up to Seven.[/QUOTE]
Thing is, they're all really good, so probably Ys I & II. It's the one that is a bit different than the others in that you run full bore into enemies to attack them, instead of pressing a button to attack.
But in honesty, you can't go wrong with any of them.
Although I heard Mask of Nepotism has some problems on the PSP, like long load times and such. I haven't played that one though, but I heard the PS2 version is the way to go.