Wings of Fire/Keeper of the Lost Cities (Wings of Fire is my favorite series of the ones you listed, but KOTLC is pretty good too.)

I read this over the summer and I liked it. Summary: Clay (MudWing) has lived under the mountain all his life, with his friends Tsunami (SeaWing), Starflight (NightWing), Sunny (SandWing), and Glory (RainWing). Together they make up the Dragonet Prophecy, and are the ones destined to end the war between the three SandWing princesses. (Well, Glory was the replacement when the guardians were unable to get a SkyWing egg, but in Clay's opinion, she's just as good, despite the fact that she doesn't have any natural weapons as far as anyone knows.) But Clay isn't sure if he wants a destiny, and when danger threatens Glory, he and Tsunami escape the cave, planning to return and rescue the others. However, the first dragon they run into out of the cave captures them and their friends. The book does have some violence, but is overall pretty good.