There is no best business. What do you want to do? Remember E2 ties you to that business for life. So think do I want to do this business for the rest of my life. Dont buy something just to get a visa or you will end up stuck with it. A modest income doesnt suffice. You need to show immigration that the business makes at least $60,000 in owner benefit. Popular businesses are villa management ( hard to get through now as a bit too popular with Brits), pool care, lawn care and cleaning, also convenience stores and dry cleaners. If you do something in the UK remotely transferable, stick to what you know.
Good business are scarce. There is a lot of overpriced dross out there which would be worth half the selling price if it was being marketed to an American or was in a different area of the US. I have heard of businesses being set up specifically to sell to some unsuspecting Brit visa applicant. So be very careful and get a good accountant to look at the books. And come over and shadow the owner for a few days and see what he does and decide if that is what you want to do.
My visa attorney would not put any businesses without proper tax returns showing a profit to the embassy, Martin.
Other than that, I agree totally with what you say. Workers comp really hit us hard. The first few months here can be very difficult, in a new country with a new business often in a field you know nothing about and with no experience at handling staff. We are just beginning to settle down after 5 months. It isnt all plain sailing though. But the sun shining in November is lovely!