Number 4 for me. Find the blue the most eye catching and ties in with the word 'Sky' nicely. It's the a natural connection my mind made. Logo looks great too!
I'd go with option 4. would like to see what the back ground for it would be in different uses, that would be the true test. How it plays nice with other elements in your brand. Cheers! Also, 4 doesn't really have the glow around the bottom half. It would need to go all the way around. Possibly some highlights in the blue up top around the elements.
Four looks the best to me! One suggestion I would ask is "have you considered a different font?" I feel like the title could be more hard hitting. Check out Sky Force as an example. Good luck!