These are all novels..  RAH was a terrific short-story writer.  That list will take longer to compile…

Presented in rough order of my rating (within each grouping).
 
Classic Heinlein:
Glory Road
The Door Into Summer
The Puppet Masters
Methuselah’s Children
Double Star
 
These are probably considered some of his “Juveniles”, but all of his stuff is readable by adults (and especially by adults who are still young at heart!):
Have Space Suit-Will Travel
Citizen Of The Galaxy
Star Beast, The
Tunnel in the Sky
The Rolling Stones
 
 
New Heinlein:
The Moon Is A Harsh Mistress
Stranger In A Strange Land (not the “uncut” version)
Time Enough For Love  (after Methusula’s Children)
JOB: A Comedy of Justice
Friday
 
 
AVOID these unless you just have to read all his books, or you are stranded on a desert island:
The Cat Who Walks Through Walls
The Number of the Beast
Farnham’s Freehold
I Will Fear No Evil
To Sail Beyond The Sunset