The subject of which tooling is better: the BBI P-51 or 21c retooled P-51 is an old debate topic that we've never been quite able to resolve on this discussion board. I think we can all agree that the original 21c P-51 tooling (from 2000) stinks, but when it gets to determining which of the other two newer P-51 toolings is "better" it really comes down to personal preference, as TKO211 noted.
The BBI P-51 tooling dates from 2004-2005. It has solid construction, great weathering, great detail markings, and fantastic cockpit detail. It comes with an excellent pilot figure as well. The pilot figure has excellent tooling, removable paracute, flight helmet with O2 mask, and crusher cap. The model suffers from a few accuracy problems including an incorrect tail wheel, the main gear do not have the forward rake, and the wing and fuselage surfaces are over-riveted. The drop tank/bomb hardpoints are designed to clip into the ammo casing chutes, which while inaccurate, can be fixed. The bombs and droptanks themselves are quite nice, with the droptanks being highly detailed right down to the fuel lines. The over-riveted surfaces that cover the BBI P-51 are less noticable on a plane with a darker paint scheme like "Old Crow" than on one that is more silver like the S1 "Killer Ace".
The 21c retooled P-51 dates from 2005-2006. Its construction is not quite as solid as the BBI plane and it is unweathered. Paint apps are generally good assuming you get a good example, but the plane did suffer from the 21c tendency to have QC defects. The retooled versions of "Big Beautiful Doll" were notorious for having uneven checker patterns on the nose, for example. Further, the first several schemes released by 21c (Flying Undertaker, Ridge Runner, & Petie 2nd) all had propeller blades with a slight bend to them - again, another 21c defect. The model has more moving control surfaces than the BBI plane and has cockpit detail that is nearly as good. The fuselage and wing surfaces are much smoother on the 21c aircraft, which is more accurate to an actual P-51. The 21c P-51 has the correct tail wheel and the main gear have the correct forward rake to them. The landing gear doors on the 21c plane have little pull-tabs on them which detract from the overall smoothness of the fuselage, however. The wing hardpoints are in the correct position, but the droptanks and bombs are more toyish than those that come with the BBI plane. The 21c P-51 pilot figure is also not the best pilot figure out there, with the older 21c P-38 pilot figure looking better.
Well, those are my thoughts. I have a couple of both aircraft and each has its positive and negative points that, in the end, sort of cancel each other out in terms of which is best. Hopefully all this helps in making your decision
