Lara is where it's at . Everyone I've referred to this one has thanked me. It's reasonably priced ($15), extremely well done. Been using this one since it came out and have had very few issues with it.
I enjoy Lara but find having a theme and making admin area look and feel "nice" should never be a companies main focus. What about regular updates and security loops holes. I would prefer for the admin theme to by always WHMCS standard versions.
I recommend being cautious when selecting a theme for WHMCS. Stick to the default themes whenever you can, as there have been many theme vulnerabilities reported lately. Stay safe!