I feed all of my fish squid along with shrimp, cut fish, pellets, etc. I don't want them to really gravitate towards one thing, because they can eventually become finicky like a 2 year old child, haha.
For my rays, however, it did become a mainstay for them, mainly because it was less messy and held together better on the tank bottom. Rays sometimes like to chew and spit, which makes a big cloudy mess. The squid was more of a chew and swallow food. Preparation was easier than shelling shrimp as well.