Personally, I would say the 3E version is better. Much broader at the least.So which Oriental Adventures should I buy? 1E or 3E? They are both on sale and with this ... going on it seems like it might be a good time to buy.
What about the OA1, 2 & 3 adventures. Were those any good or did they have interesting material?
I can't make a recommendation on the adventures, despite owning them. I found the Kara-Tur boxed set and its adventures a bland mirror that tried too much to be "historical" (and failed), so I never actually ended up using them. I'd look for Legends of the Five Rings books/adventures - as Rokugan was featured as the 3E campaign world several of their L5R books and adventures are dual system so you can use them with L5R or D&D 3E. (Personally, I prefer the L5R system & world).