I agree with Wayne and Jan, both are very good, but the Hasegawa has the edge I think. The props on both are slightly 'heavy', but nothing some gentle sanding won't cure.
As for the Testor's kit, I built the same kit released under the Hawk lable, the 'plated' version, about 25 years ago. Apart from the plating, overall it wasn't bad, for the time. It needed some detail addidng, and the undercart as I remember was a bit basic. However, the biggest problem, which was true of virtually all kits of the P51D, in all scales, until fairly recently, was the cross section of the fuselage,particularly in the cockpit area. It was either too narrow, or too wide, both being a common problem. I seem to recall it was the former, but this was only visible from certain angles.
The Revell (ex Monogram) P51D is not a bad alternative, with some fairly good basic detail, but the moulds are showing their age now, and you would need filler around the lower cowling, whiich, for some unknown reason, is a separate part.
Order of choice, for me, would be:-
Hasegawa,
Tamiya,
Revell.
Hope this helps.
Terry.