I love the picture of the "Snarl" on the cover. It's awesome!
My favourite font is on the second cover - the one with the lighter blue background.
Having the blue in the background is pretty cool and I like the darker blue on the final sample, but I'm not completely sold on it; the watercolour leaky/splotchy look doesn't do it for me.
I know you're earlier
Heart of Rock is complete, but just wanted to mention that I really liked the final one to put together with the grey rock background. I understand why you went for the fun and friendly green background but I much preferred the grey. It looked classy.