Done all Len Deighton. Gavin Lyall, Sherlock Holmes,, Campion Sayers.
History based would be nice. Enjoyed Bernard Cornwell Sharp and US Civil War.
Liked some Georgette Heyer, Toll Gate and Reluctant Widow have unique plot devices. At least I have not seen them before.
Not liked Sci-fi, Fantasy etc.
I like to suspend disbelief but have to be almost possible for me.