Hey Kris - Whey protein is packed with more amino acids which can help boost the immune system. Whey protein also gets absorbed more than Soy. I have tried both and can honestly say that I get bigger and put more weight on with Whey protein. Whey also packs a little more calories, rebuilds cells, and usually boosts more energy. Make sure you get 100% natural Whey (which is usually made from cow's milk, egg whites, etc.)
My dad is finally starting to feel better today. He has to go back in for chemo next week though for 7 days straight...then he gets to come home and feel like crap for a week, ughhh I hope all is well with yours :)