The Heller F-84G is gray injection molded plastic. The kit has raised panel lines. I don't know if this or the AGA/Plastyk/Inplas kit came first, but it appears from inspection of the parts trees that one used the other as a guide to parts breakout, as each tree has generally equivalent parts. That is not to imply the quality of the AGA is equivalent to the Heller kit, because, although the Heller is not a great kit, it is a good kit and at least reasonably accurate where the AGA is not. I paid $3.00 each for these two kits; I have not investigated retail or collector prices.
There are 44 gray plastic parts on four trees, six clear parts, and one decal sheet. The parts are well molded with little flash present, the raised panel lines are about as fine as can be done on a 1/72 scale kit, and the canopy and windscreen are nicely done. However, the bracing tape on the aft centerline of the canopy is missing. Though there were variations in bracing tape application as the process evolved, I have not seen any indication of a pattern where the aft centerline tape was not installed when the other transverse and longitudinal tapes were present. The decals are slightly out of register, but otherwise quite good. Markings are furnished for two natural metal NATO aircraft, French 1-N1, serial number 51-10955, and Norwegian F-FN serial number 51-10145. I have not built one of these kits, but general inspection and dry fits show the parts seem to fit well. The primary defects are wing tanks slightly too small, fin slightly too large, and sparse to no detail in cockpit. For fuselage differences, see 72nd scale kit fuselages compared.
The Heller F-84G kit is generally the defacto standard for this aircraft in 1/72 scale, unless the AeroMaster kit with the resin and photo etched upgrade parts is considered. Since I haven't yet seen that kit, I have no basis for comparision. As for comparing this kit to the AGA kit, there is no comparision favorable to the AGA; my opinion is don't waste your money on the AGA/Plastyk/Inplast -- even if it is only 4-5 bucks, it isn't worth it. All things considered, the Heller is not a great kit, but it's not too bad either -- and there are aftermarket decals available. UPDATE 1: Since the above was written, Tamiya released their 1/72nd scale F-84G kit #60745. That kit is a step up from this Heller kit; see the reviews by Bruce Craig and Drewe Manton. UPDATE 2: I recently obtained an AeroMaster kit, and it is reviewed elsewhere on this site. UPDATE 3: Another new 1/72nd scale Thunderjet kit was released by Academy. It is slightly better even than the Tamiya kit, and is reviewed elsewhere on this site. Because the Tamiya and Academy kits are the kits of choice and are so much better than this kit, I have downgraded it from a "7" to a "5."