Since taste is subjective, I'd encourage you to try several brands and flavors to see what you like.
Having said that, I'd highly recommend Killer
juice. Walt is committed to providing a high-quality product at very competitive prices and his customer service and responsiveness are excellent (second to none, in fact). To top it all off, his sales are unbelievable (he had 5 flavors at $0.99 per 15mL bottle and 5 at $2.49 per 15mL bottle last weekend).
KJ offers no caffeinated juices yet, though...Walt is experimenting with them, but not ready to release them yet.