The vast majority of an adult domesic rabbit's diet should be grass hay. It is best to offer a buffet of grass hays...timothy, orchard grass, brome, oat, etc....and you can offer different cuts. Hay does three major things. First and most important, it maintains a healthy gut.....low protein, high fiber. The hay is the roughage required to regulate GI transit time. It is the pressure that keeps thing moving happily along. Hay is also the primary way the teeth are kept to a proper length....assuming proper dental occlusion. Long strand hay is best. It is not how hard something is but how chewy it is. And by feeding a buffet of hays, you promote a more natural foraging type behavior and it gives them something to do. Hay should be availabe at all times. And contrary to popular belief, some alfalfa hay is good for them. Many people believe that alfalfa contains too much calcium (and there can always be too much of even a good thing) but rabbits have bones and teeth and need some calcium....and Vitamin D and Phosphorus to aid in absorbing of that calcium. My primary concern with using too much alfalfa is weight gain.
Pellet amounts, compositions and brand vary wildly. We use pellets only to maintain body conditioning. We have a pair of bonded Flemish Giants....they get about 1/3 cup pellets per day to share. We have some smaller breeds and some that have weight issues on hay only (along with appropriate supplements). Many aruge that only timothy based pellets should be used. If fed properly, the amount of pellets should be so small that it should not matter how the pellet is based. Brands of pellets are a matter of personal and bunny choice. Many people consider Oxbow to be the best....I do not share that sentiment at all. Some are huge fans of American Pet Diner pellets. I have not used them but the other products I have purchased from APD have been very high quality. And some regional farms also offer a "house" brand of pellet.
We do offer limited greens.....romaine lettuce, parsley, cilantro, Spring Mix, dandelions and carrot tops are a few. A small piece of fruit every now and then won't hurt....note "small". We have offered banana, strawberry, peach and orange to name a few. The key is small portions.
Always keep in mind....low protein (meaning limited high quality pellets) and high fiber (unliminted grass hay) is the rule. Offer veggies and fruits in small amounts....and only one at a time. Make any changes in the diet over a period of several days. Good luck.
Randy