I put down China, mostly because of the variety (Wuyi, TGY, dancong), but also because I lurrrvee me some Wuyi yancha. I do enjoy Taiwanese oolong very much, but Taiwan's range of oolongs doesn't seem as diverse.
Upton Jade Imperial from Taiwan is about the craziest-ly great beverage I have ever had. I almost feel foolish liking it so much because it is almost not tea--to this palate that was raised on black teas and restaurant oolongs. Clear yellow with the flavor and aroma of flowers..and little else..and ZERO tannins. Can tea have NO astringency and still be tea?
For something more 'regular', I think the Chinese oolongs are maybe my first choice.
Technically, there are no tannins (except for trace amounts) in any tea– polyphenols are what give tea its astringency, unlike wine which has tannins. That's beside the point, though– I'm glad to hear you liked it! You might want to try Adagio's pouchong (aka baozhong) if you're looking for something else like that.