Mine eat romaine, green/red leaf lettuce, and parsley almost exclusively. I like romaine because it comes in large heads and stays fresh for at least a week. They love their parsley, and I like having it around so I can grab a handful and cook with it. Sometimes they get escarole, but I yell at DH when he buys it because it’s way more expensive than the other lettuces 😉 Chicory is a good lettuce too, though they don’t seem to like it as much.
Beyond that, they get things we have sitting around and need to use up, especially last summer when we got all sorts of random things from the farmer’s market (beet tops, kohlrabi tops, arugula, etc). We also buy the big boxes of mixed greens for salad and if we have any left at the end of the week the bunnies get it with their dinner. They also get any herbs I buy for cooking and don’t completely use up. They’re great for cleaning out the fridge sometimes! Haha
eta: I should mention that Otto is fairly picky, which is why I usually limit it to only the lettuce and parsley. Most of the time anything “different” just gets eaten by Hannah. He also gets poopy butt occasionally, so I try to limit the new foods in his diet. Just have to work with your rabbit and what they like, sometimes.