Thx guys, as always, very helpful. I did assume already that most 1 cover 4*s don't make a big different (except for Ghost, Miles and Invisible Woman where I go the "invisible" cover), but I am already trying to focus on how they can help me in the future. Like, I was so lucky to get 3 covers for 4* Carol in a short time, then she featured in an alliance event, and now I have her with 5 black covers (and one saved already...) and 2 yellow, so she's extremly helpful already. Still hoping for that 1000 HP from DDQ every day to get more 4*s in
Another question: Is there a file or a thread somewhere, where you see which 3*s feed which 4* and so on? That's also helping in deciding which 4* to keep.