SR71 Avro Vulcan Yak-1b La5 FW190

No Habu? (https://upload.wikimedia.org/wikipedia/en/f/f2/Early_project_logo_Habu_SR-71.jpg)

Definitely the SR 71 and the T 38 trainer

SR71, P38, Mosquito, Avro Lancaster, F104.
Totally agree with the Spitfire, best looker - ever

DC-3, Hughes H-1

So many possibilities I love the P 38 and Mossi from WW 2, Me 262 too as well as FW190. More modern there are the simple lines of the original Sabre and Mig counterpart, F4 and Vulcan. F16 probably one of the best from last 40 years. B 1. so many hard to pick 10.

The list is now well beyond 10, but let's also add Hawker Hunter, Piaggio Avanti, and...Edgley Optica.

Well "the most beautiful" is so subjective, but I agree for Connie in first, though i'd prefer the 1048 super Connie, even more "beautiful" ! Lookhed P 38 forgotten IMO... and some other ! Thanks anyway

Like many other commenters, I say you missed the mark by not including the SR-71 Blackbird. The most beautiful aircraft ever built.

I don't think the P51 was developed to replace the spitfire - The RAF required aircraft to bolster their numbers at the height of the battle of britain and asked the US for help by supplying the already in production P40. on paper the mustangs only improvement on the spit was range, performance wise they were very close but the spit had slight advantage in manuvrability.
I would also say the Mosquito is certainly on the top 10 list though