My cats are having HUGE and VERY SMELLY poops?

I have 3 cats ages 5, 4 and 1. The littlest and oldest have always taken what I feel to be abnormally large poops for a cat from time to time but since I became pregnant (yes my boyfriend does all the litter changing now thank goodness) we haven't been buying them the expensive pet store brand food (Nutrience) that we had been trying after hearing Iams was no good anymore. In its place we have tried grocery store brands like Whiskas and Purina but my cats are taking ENORMOUS gag worthy craps now :( I am talking stink up the whole apartment for an hour afterward poo here it is terrible! What is the best kind of food that you find your cats can digest well and not give off so much waste. I understand why my cats are so hungry all the time it's because they are clearly not getting what they need from these cheaper brands. Is Nutrience a good food? we were just starting to buy it before we switched but they seemed to like it, what are some other good brands? I'm willing to pay more so my cats, boyfriend and I can all be happy again!