I've never played the actual cart, but tested this out on a friend's ROM-filled Xbox. So I'd go along with this as worst.
However, if I were counting only games I'd legitimately played, Suzuka 8 Hours on SNES gets the honor of worst game. Ugly mode 7 effects, simplistic backgrounds, terrible sound and wonky gameplay. I rented this and spent less than 5 minutes on it before tossing it aside for the rest of the rental period.