Classic aircraft
First on my list would be the Dakota. Still in everyday use, and reliable as ever, if you can shut the door on the cargo it will still take off...
The Spitfire must share honours with the Hurricane; our Continental friends might nominate something different from that era.
Third, the Catalina.
Fourth on my list would be the 747. Alas, the Concorde never proved so enduring.
And fifth, my own PA18, now being flown at White Waltham. I miss it so much. Slow flying over the summer scenery, with doors wide open, banked right over to starboard for the best effect... Piper Cubs first designed back in the l930s, and still used today tugging gliders, banners, flying on floats and skis, the chariot of choice for Alaska, or Africa for that matter.
What's on your list?