Like you said, it is not easy to give a generic "one size fits all" kind of answer. But I will give you a few specific things to think about based on what you said.

1. I would say choose the company that fits what you want/need especially at this point in your career when you are 35+ with 20 years of experience. Put yourself first. Now you are saying that you are much bette at hands on. Then choose the company which provides you that option. I am guessing the company B in your scenario. Of course there is an element of risk involved in a startup but then again, no risk no reward. You don't want to be miserable in a job at 35 which you don't like.

2. The other side to it is that in a large company, you will definitely have the opportunity to meet a lot more people (talented and otherwise:) and perhaps build a great network. How much do you care about that at this point in your career ? You have worked for 20 years and I assume you have a good network already. Yes u can always do more but may be thats not as critical at this point.

Hope this helps and gives you some perspective.