Hard to say really.. There are two models I built that 'changed' the way I scale model, but both were scratchbuilt... The first was a 1/72 Aviatik D.I Berg, my first ever scratch, with the 'how to' article from a now long defunct (
) French magazine called MPM. That really changed my views on what I could achieve from the hobby. The second was a 1/72 T3 Christie that I scratchbuilt following the publication of a similar article in FSM. The article dealt with a 1/35 scratch model and I tried to outdo that by making it smaller yet all open, with the crew areas, the engine, transmission, weapons,.. This model got me my first scale modeling commission, in 1998.
In terms of kit, then, my most important kit was the result of that first commission, an Autoblinda AB41 in 1/76. It was the first kit I ever designed and that got marketed (by SHQ).