To date I have built three of the Italeri M8/M20 plastic kits, and I had no issues what-so-ever assembling them together. In fact, I think they are pretty good kits. Of the three, two were produced for Warlord Games (black box), and one under their own name (green box). The plastic is exactly the same, but the decals are different.
To date I have built one of the M8 plastic kits from Rubicon Models, and this is also a good kit.
Which one is better? I'm only going to say that both are so much better than the resin piece of crap that was only available to us until plastic kits were released.
I said this in another post, but its worth repeating. I remember a time (not so long ago) that the only 1:56 scale vehicles available were resin! And even some of the worst plastic kits are better than most if not all of those old resin kits.