I guess I'm a little old school. I looked at those interlock plates that you screw onto your breaker panel cover plate and then backfeed the panel through a 220 breaker. I know they meet Code in most areas. I also talked to three different electricians about those plates. The two younger ones said they work great and I'd be foolish to waste my money on a proper whole house transfer switch. The older, more experienced electrician (a personal friend who has retired) agreed they meet Code, but he would never install one. He has seen too many things happen to trust isolation to a breaker in the panel. There is no way to know what can happen to the utility system during a severe storm. Utility lines can get shorted, voltage can go way high momentarily (say a transformer switchyard has a problem) or the neutral leg can get energized.
In other words, things can happen outside the home that a 220 breaker mounted in the panel is not designed to handle. A interlock plate is designed to protect the utility lineman working to restore power. It is not designed to protect your house.
I believe a separate transfer switch panel provides superior isolation between the house and the utility. Throw that switch and I don't care what happens with the utility lines. I'm isolated.
So I did it the old fashioned way, 200 amp manual transfer switch. People have told me I wasted my money. I'm ok with that.