Hatfield House or Sissinghurst? Or other?

We stayed at the B&B run by British Trust at Sissinghurst--may be too late to book but the gardens are nice. If you have a car I would suggest Chartwell and there is also the Kipling house and Knole.

I can't say which one I prefer because I haven't visited Hatfield House even though I lived in London within easy access. Sissinghurst is spectacular, and probably the most admired garden in England, but really no interiors to look at. Hatfield House is closer to London with direct public transport links, something Sissinghurst can't match.

Sissinghurst is more of a grand farmhouse with a tower-keep in the middle of the grounds. The gardens are lovely and quite extensive.
Hatfield House is more of a grand manor with loads of history connected to it. Elizabeth 1 was staying here when she found out she was queen. The family still lives in the house and it's nice to see things like ping-pong tables set up in the armory for their teenagers! The gardens here are also quite stunning.
Personally I prefer Hatfield since the house is grander with exquisite gardens.
Highclere Castle is within fairly easy reach of London. It's a very stately home with some very unique features and lovely gardens and grounds.

I ended up going to Hatfield House yesterday and absolutely loved it. Beautiful interior, lovely gardens. Highly recommend it, and only 25 minutes from Kings Cross!

Good to hear. Must get there when next in London. The travel time would have definitely swayed me.