I agree with bambooforest, on some level, I too, don't feel like I've had enough teas from different regions to make good judgment for myself.
Yet, I chose Shizuoka (mostly Honyama) - by far my most favorite teas have come from here. However, this is only because I've had (by far) the most teas from here. That will hopefully change in time.
Outside of Honyama, I really like Yame (Fukuoka). I have had so little tea from Kagoshima (just 2011 YM and Chiran Sencha, which were both very good), so it's hard to know. The gyokuro I've had from Uji was excellent, but the sencha didn't compare to the other regions. As I said though, I have very little to go by (O-cha Kirameki was very good, but Maiko Maruyama was not so good, imo).