You could also call the shelter and ask them what they feed, dietary changes can be stressful for cats, so if the shelter feeds mostly donated foods, it's probably something like Friskies (if they're lucky) or generic store-brand (if they're not). We average around 60-70% Special Kitty and 30-40% other foods. It may be easier to change their diet if you start with what they're used to. They may also just be reluctant to eat if they've just come home, just because they're stressed.
That said, SciDiet does taste pretty yucky (at least the ones I've tried). There are a ton of threads here about what's good food. I personally liked Wellness and Innova dry (because I could get them where I live), as my cat has issues with corn and both of those are corn-free. I prefer an all (or mostly) canned food diet because I think it's healthier and more logical for cats, but you'll have to make your own determination there. I have my own criteria for choosing foods, but basically, I look for named meats and meat meals in the first three ingredients (as opposed to, say, "meat" or "poultry," I want to see "Chicken" or "Beef"), no by-products (this is a grey area, and I've not yet found a cat food that I think uses a balanced amount of byproducts, so I avoid them altogether). I look for foods with absolutely no corn, wheat, or soy, and prefer one that uses whole grains. I also avoid things like BHA, BHT, ethoxyquin, and additives that I believe are unhealthy. My cat has further dietary issues, but if I was looking for a solid, basic maintenance food, that would be my initial set of tests.