They are all very different....so it depends what you want!
Thrill on the Hill is special, but you do run the risk of bending your P&J...
Silverstone Classic is all about watching racing
Blenheim is a day to natter to Morgan owners, look at other peoples cars and help raise money for charity.
Me, I'd do TOTH and Blenheim, I'm not a great fan of watching other people drive round and round. BUT we all differ....