J.X.
I'm an interior designer (or was one before being a SAHM). This is really an asthetic choice more than a durability issue. Knotty alder is a very casual county/ cabin look. It can look great if casual, country is your asthetic. What about the color? Does it work with your other wood tones or does it introduce a whole new wood tone? Do you like it? Does it fit your concept (assuming you have one)? If you like it and it can work with your interior, push them for as many upgrades as you can. But at the end of the day, you have to like it, so don't settle if they made the mistake. Personally, I don't care for oak cabinets because the wood grain is usually too busy on a vertical surface. And while oak is much harder than alder for scratching, its not a floor, so scratching won't really be an issue. Perhaps you would want to email me a photo of the kitchen and the flavor of the rest of your house? Send me a personal email if so and I would be happy to do that.