The only ones I managed to max so far are a couple of the legendaries. I added them to my main account instantly, and they're awesome. My common, rare and epic cards are more or less gold league level, and I was in doubt about adding them to my gold league deck for a while, but instead, I decided to delegate them to a separate account so I could learn about their abilities. Quit a lot of info to wrap my head around, and I'm a slow learner, lol.