It's really personal opinion. I feed oxbow because it's the only decent rabbit food available in this country. I pay an arm and a leg for it, but having one rabbit means it takes a while to go through a bag so I'm not overly fussed about price. I've heard people rave about the benefits of both brands, but I'm honestly not sure if one is superior to the other.
Really the main thing you can do is compare fibre levels etc and the ingredients list. Sherwood forest has far fewer ingredients, but the pellets seem to be alfalfa based, whereas oxbow are timothy based.
Sherwood Forest Adult:
Crude Protein min: 19%
Crude Fat min: 6.5%
Crude Fibre min (max): 18% (23%)
Moisture max: 10%
Calcium min (max): 1.7% (2.2%)
Phosphorus min: 0.6%
Salt min (max): 0/85% (1.35%)
Copper (min): --
Oxbow Essentials Adult:
Crude Protein min: 14%
Crude Fat min: 2%
Crude Fibre min (max): 25% (29%)
Moisture max: 10%
Calcium min (max): 0.35% (0.85%)
Phosphorus min: 0.25%
Salt min (max): --
Copper (min): 30ppm (parts per million)
Sherwood Forest Ingredients:
Sun-cured alfalfa pellets, proprietary whole oil-seed blend, monodicalcium phosphate, choline chloride, essential amino acids, chelated minerals, B-vitamins, cobalt carbonate
Oxbow Adult Ingredients:
Timothy Grass Meal, Soybean Hulls, Wheat Middlings, Soybean Meal, Cane Molasses, Sodium Bentonite, Soybean Oil, Salt, Lignin Sulfonate, Limestone, Yeast Culture (dehydrated), Vitamin E Supplement, Choline Chloride, Zinc Proteinate, Zinc Sulfate, Ferrous Sulfate, Niacin, Copper Sulfate, Selenium Yeast, Vitamin A Supplement, Folic Acid, d-Calcium Pantothenate, Copper Proteinate, Riboflavin Supplement, Manganese Proteinate, Biotin, Manganous Oxide, Thiamine Mononitrate, Magnesium Sulfate, Vitamin B12 Supplement, Sodium Selenite, Pyridoxine Hydrochloride, Cobalt Carbonate, Vitamin D3 Supplement, Calcium Iodate