Most valuable toy: Devilgotchi (approx. $400)
Original price: $17.99
Selling for now: $18-$200
Some Tamagotchis go for upwards of $300, but odds are that yours doesn't. There were over 40 versions (lines) of Tamagotchi released, and each line featured a variety of colors and variations. Only about 20 Tamagotchis are listed at over $100 on Amazon. Of the 79 million Tamagotchis sold, yours would have to be one of the rarest models to be worth the effort of resale.
Due to the large number of Tamagotchis available and the relatively small number of hardcore fans, there seems to be a lack of consensus as to how much rare Tamas are actually worth. TamaTalk, a Tamagotchi fan site, has a number of forum threads dedicated to determining a fair price for a vintage Tamagotchi.
It's generally agreed upon that the Devilgotchi is the rarest Tama, though there is disagreement as to what the Devilgotchi is worth. A recent eBay sale went for $360:
And an unsold listing was marked at $589.
This tells us that the best guess for Devilgotchi value is somewhere in the neighborhood of $400.