I am a UK-USA dual citizen who grew up in the UK but moved to the States thirty years ago. My US citizen husband had been offered a job back in London. Do I have to do anything special as an ex-pat to return to the UK? And is it best for my husband to join me on a spousal visa or through a work visa?
You don't need to do anything special to return. As far as which visa is preferable for your husband, it probably makes little practical difference once the visa is granted. In both cases, if you intend to stay in the UK long term, your husband will need to extend his visa once, and then apply for indefinite leave to remain after having lived in the UK for 5 years. The benefit to your husband of the family visa is that he can change jobs without having to apply for a new visa.
However, in order for your husband to be granted a family visa, you (not your husband) will need to meet the financial requirement. This involves proving you currently make at least £18,600 a year, or have £62,500 in cash savings, or a combination of the two. If you're unable to meet this requirement, then the Tier 2 visa is the only option.
On the other hand, for your husband's employer, it is likely preferable for him to apply for a family visa. Tier 2 visa applications are limited, so his employer may prefer to save their allocation. I'm assuming that the company will be covering the application costs for the Tier 2 visa, and he might want to discuss with his employer if they prefer him to apply for the family visa instead, at the company expense.
The third option would be to initially apply for the Tier 2 visa, and then when it is time to renew, switch to the family visa. In this case, you'll be able to use joint income to meet the financial requirement.
Just apply for a current UK passport if you don't already have one, and that's it. Your husband should apply for a Family Visa.