Eh. Thats a tricky one. Although, I prefer Shelby over the old furby(Shelby says more things) But the new furby can learn the entire dictionary. O_O (Or atleast, thats what I've been hearing from people that own one.) Tamagotchis are cute and fun at first but can quickly get boring but I've been a Tamagotchi fan for a long time. But tamagotchis just beep... And move around on a tiny sceen. Usealy, the games they have average around 1-6 and once you've played them all, it gets boring. Sure, I love tamagotchis it's just that... Furby can do more things and it feel more like a real pet then a tamagotchi. Although, I wish a furby could die so you could take more intrest in takeing care of it.
So, I'd have to say Furby. Even though they're loud mouths but you can teach them more things then a Tamagotchi could.