Best one for seeing the shields personally I've felt has been Klingon. However I wish it would let me change the box outlines of enemy targets. I'm far too used to friendlies being orange and enemies being yellow. But yeah, current new UI makes things harder to see.
Plus I really like the old Red UI as it currently stands for KDF. Very easy on the eye. Tried Fed Blue and vomited.
Quick Edit: Should point silverfaustx, you've taken beef with a lot of potential issues. Thought about making a detailed list?