I really think this depends on your personal situation. I know there has been a lot of disappointment expressed regarding legendary souls. I've only opened two of them. I got a Regular Eddie (ouch!) and an AOP. I got my third one a couple nights ago (1000 SLs) and will open it tonight.
I don't play the arena much, just enough to hit the daily challenge and maybe a few extra per day sometimes to pick up some coins. In my own case, I intend to use coins exclusively for legendary souls for the time being. The reason for this is that my roster has very few native 4* and 5* characters, so the likelihood of a dupe is pretty low. I also have quite a few skill shards saved up waiting to be used on the right character(s), so I'm not feeling a lot of urgency to add more to the stockpile.
druid138-6195