There’s loads of aircraft which I’ve bought which I don’t really fly very often or indeed ever. I don’t think it’s fair to say they’re the worst. They’re just not for me. The Twin Otter isn’t perfect and was over hyped but it’s no where near the worst thing I’ve paid good money for.
The Eurofighter Typhoon is total garbage. That’s probably the biggest waste of money. I bought that Storm add on from flighrsim.to. Nice idea but it’s poorly done.