There are different types of casinos; instant play, download and mobile. I always prefer it when I'm not required to download a software so as to play. It is easier playing on the go and that's why I prefer the instant play or mobile casinos.
I agree that the non-downloaded type is the best for us on-the-go people. Sometimes the downloads are lengthy and I don't really like them having access to my computer whether they really can see anything or not. Just being cautious.