This is a tricky question. There are scientists studying the relationship between the number of taste buds on a person's tongue and how strong someone's sense of taste is, but these studies are hard to do in animals because we can't communicate with them.

These same researchers are studying taste buds and taste sensitivity in rodents (rats, mice) using behavioral cues (licking speed, for example), but it's hard to tell if the rodents share the same tastes. We know that rabbits have extra taste buds compared to humans. There are two structures on the tongue that carry taste buds: mushroom-shaped lobes ("fungiform papillae") and leaf-shaped lobes ("foliate papillae").

Humans only have taste buds on the fungiform papillae, while rabbits and related animals (hares, pikas, and conies) have taste buds on both the fungiform and foliate papillae.

The tongue of the Florida manatee is similar to rabbits as well. All of these animals (rabbits, hares, manatees) are vegetarians and eat a diet that is pretty different than ours. Can you imagine if your nose was three or four inches from the ground and you just ate what was in front of you?

A lot of plants are toxic, so my GUESS is that rabbits have well-developed taste buds in order to detect bad-tasting, potentially toxic food and avoid it. (Many times toxins are bitter-tasting.)

Vegetarian animals have a hard time getting enough salt (think of all the salt licks ranchers provide cows). So rabbits can probably detect salty from bitter. Whether they can detect sweet from sour I don't know. If you had a rabbit as a pet, you could experiment with natural sweet things (strawberries, grapes) to see if rabbits prefer them to lettuce or celery. Carrots are actually pretty sweet, even though they are a vegetable, since they have a lot of sugar, so if your rabbit likes carrots, it may be that she or he can taste sweetness and prefers sweet things. Humans have a natural preference for sweet foods (most of us) but that might not be the case for rabbits. You should check.