The adult food is an alfalfa base, has beet pulp 14% protein 25% fiber 4% fat 0.6% calcium The house rabbit food is a grass base, has thyme, no added sugars(eg beet pulp) 14% protein 22% fiber 4% fat 0.6% calcium. The 4+ is an alfalfa/timothy base, has thyme, no added sugars, added vitamin C(not sure why they think older rabbits need that added) 12% protein 22% fiber 4% fat 0.6% calcium. Both have other similar ingredients(wheat, soy, peas, linseed, prebiotics, yucca) except the 4+ doesn't have prebiotics and yucca.
Not sure why they think older rabbits need lower protein. It's usually the opposite. The older they get, the harder it can be to keep on weight so they need a higher protein feed. I don't see any reason to feed the 4+ food unless you have a rabbit that packs on the weight and you need a lower protein feed and can't just reduce the amount of pellets fed to reduce calories.
The adult food is better in that it has a higher fiber content, but the house rabbit food has a grass base and no added sugars, so likely a lower carb content, which is a good thing. Ideal would be the higher fiber from the adult food and the no sugars from the house food.
So it's just a matter of either preference or what works best for your rabbit. I imagine the house rabbit food is more expensive, so there is one consideration. If cost isn't an issue and you aren't sure if you want to stick with the adult food you are currently feeding, both could be tried out(transitioning from one to the other correctly) to see which your rabbits did best on. The no sugar one might be good for rabbits with sensitive digestive tracts, and less pellets and more hay can be fed to make up for the lower fiber. Otherwise the regular adult food is probably just fine if your rabbits seem to do well on it and have nice healthy looking poops. If they do, then I would just stick with the adult food. It's cheaper and you won't have to go through the hassle of changing foods.