Red and black stars are very calm and loving. So are the ISA browns and all give a good quantity of large to extra large brown eggs. The ISA Brown lay early and longer and don't go broody so if that is important to you go for them. The Stars are more like a heritage breed, as they are a heritage cross, will go out of lay to molt sooner and may slow up considerably in hot or cold weather. So they may go broody too, do you want them to be hatching out chicks for you or would you rather have a steady egg supply and use an incubator if you want to hatch? Stars are bigger birds and can be used as a dual purpose if you want to hatch chicks for meat birds too. Just cross with a heavy roo.
EDIT to add that the ISA brown being a smaller bird needs less feed, and as they lay longer you get a way better cost ratio feed/eggs if that is important to you.