Out of this, DW2, and DW3, I'd say it's this one, simply because it's a unique experience. DW2 and 3 are standard RPG fare, and that's been handled a lot better elsewhere. DW3 isn't bad but the second game is pretty awful.
Why aren't I drinking today? Why don't you shut up before I get so angry I need a drink?
Digimon DS games are mostly fail, probably because they mimic the gameplay of most Pokemon games. I'll probably play Digimon World DS if I could choose amongst all the Digimon DS games.
DW1 is one of its kind, as original as it can get (from the original Pendulum keychain). Even though the digivolutions might seem weird, they are the closest to the true/original digivolution (before DW2/DW3 made more popular/fanboy lines). Unlike most other RPG games, DW1 gives you the freedom of choice. You can do whatever you want, when you want, so there is no 'one correct way' to follow.
I would probably play DW3 also, since it's a much bigger world compared to DW1 and the gym features of DW3 are pure win. You don't have to catch them like Pogeymans and unlocking different Digimon with your levels is rather nice too. I guess I like both DW1 and DW3 equally.
This was the only Digimon game that I've played which has been most true to Digimon's roots. Probably because it was made before the Digimon anime series came into existence, and every game afterwards seemed to cater almost exclusively to the anime's weird canon. That's fine for most people, but I am a fan of the Digimon as they were orginally: Keychain virtual pets. This is why Digimon World was the best Digimon game for me.
-First things first, but not necessarily in that order.- -Everything we've ever stolen has been lost, returned or broken-