I've been waiting for someone to mention magit. It is the only UI I know of that is more than just a git shell. Real thought went into it and it shows. It is faster and more convenient than the command line, which says a lot.
It's still not as fast as vim-fugitive for example. I know magit does more in nicer ways but the delay when staging, for example, is noticeable and can be annoying over time.
I'm not sure I follow. I hit s on my file in the Magit buffer and it's staged instantly; what delay are you referring to?
On my machine it takes like 400ms until it's staged.
When working in vim, staging really instant.
I stopped following magit closely after the big rewrite, but magit is goldmine, so lean and so mean.