The adult rabbit formula has a better than average fibre content which, given bunnies are herbivores/fibrevores, the more fibre the better.
Oxbow is one of the best brands of pellets for small animals or pocket pets. A good quality pellet has important vitamins & minerals that the bunny misses by being a house bunny or caged bunny. Don't buy any pellets that are lower than 20% fibre, they are just no good at all for your bunny unless you want it to gain weight, but there are better ways of increasing weight in an underweight bun than by feeding them junk food. Your bunny-savvy vet will help here.
Pellets ARE NOT the main source of nutrition for bunnies. Bunnies should be eating a diet of mainly good-quality hay, such as oaten hay or timothy hay. A pellet-only diet will mean a fat, sick bunny.