You've probably fallen into the trap that many newer players seem to BillyBones... playing the game basically only one way. Why do I say this? Because there may exist a "best" trait-UU combo given a basic playstyle, a basic map type, basic opponent roster, and a desired victory condition.
However, there exists no best trait-UU combo. The game works as far too complex and varied for that. For example, very few players would say they like Portugal's trait-UU combo. But, given the right conditions for an upper level 20k (but not Sid level) and some decent luck, they have REALLY good traits without really needing SGLs. Check some of my HoF games. So, leaving out Henry doesn't make any sense.
By the same token check lower level spaceship, diplomatic, and even 20k games HoF games. You'll find Cathy plenty of places there. Expansionist and scientific make for especially fast research when you can pop a lot of huts. Expanionist can get you a free settler and scientific works well for getting SGLs in a 20k game. On top of that, the cossack makes a good leader spawning tool for the Heroic Epic since it has blitz. Go Russia.
A team of Sid virgins deliberately selected Gandhi and his trait-UU combo for a Sid pangea game here
http://forums.civfanatics.com/showthread.php?t=108916
If I only played histographic games for score, I'd probably pick Smoke-Jaguar most to all of the time, but I'd have to dream up a really strange scenario where I'd pick the Maya over a scientific tribe in a spaceship game. I could give you many more exmaples.
So, with that said... what sort of victory condition, map type, start, etc. do you have in mind BillyBones?