I like the PCE ones a lot, but that's because I love the music in the PCE versions a lot. I played the Master System games first, then the SNES/SFC games, then the NES/FC versions, and I sporadically played several other versions of Ys games from most of the systems they were released on. A lot of games really tried to use the Ys formula after it was released in 1987. It's one of the more important computer-based RPGs in history, so it's good that people are getting into it now. It focused a lot on player precision despite fighting enemies at an angle vs head-on.
The PC-xx01 versions of the game/X68000 versions of the game are a little more difficult with respect to hitting enemies, while the console versions of the game (and later PC versions) are a little more lenient with respect to hitboxes. But what I like about the games is that they respect your time. They don't bs you while letting you explore around the areas adequately while being completely straightforward.
Ys 1/2 were top-down. Ys 3 SFC/FC shifted the perspective to being a side-view (think Zelda II). Ys 4 (both versions) went back to top-down. Ys 5 gave Adol a jump and attack buttons which was a surprise. Ys 6 was the first 3D entry, and Ys 7/Celceta brought parties into the mix.
Overall, I'd recommend Felghana and Origin to newcomers since they're much easier to get into than the original games that I played, and they feel much tighter. If you're going to play 1 or 2, I'd go with the PC version of it. If you play Ys 6 and want to play the localized version of it, go with the PS2 version over the PSP version unless you get access to the PC version. The PS2 version has extras. The PSP and PC versions don't. The PC version looks better, though; and there's a fan-translation for it out there.
Never play Ys 1/2 DS. That version sucks ass and is the worst version of 1/2 that I've ever played. Ys Strategy, the JP/EU-only RTS Ys game for DS, is pretty bad, too.
With respect to Ys 5, that's Japan-only, and if you actually want a challenge for it, I'd go for the Expert version than the vanilla SFC version.
I don't like the formula that Ys 7 and Ys Celceta followed, really. Not what I look for in Ys at all. But a lot of people love those games, so maybe it's just me being old. Like, I like Nayuta no Kiseki because you know what you're getting into: a hybrid of Ys and the Kiseki games so you expect more narrative and two characters to use in battle who play dramatically different from each other... but you have platforming and Ys 7 took out a lot of the platforming and more difficulty and added more story than I liked. The games were never really known for having an elaborate story and focused on the ARPG elements first and foremost, so them starting to have more story is a little awkward for me, having played them longer. Ys Celceta was... a very weird version Ys 4. Ys 4 is in this weird, awkward position where there are multiple versions of it, but at the same time Celceta felt very much like Ys 4 in-name only.
But the long and short of it is to play Origin/Felghana, preferably on PC.
