Hey mate, welcome to the forum. The 4.2 is my pic of the bunch, but as with most things that is just an opinion. As said above some years of the ZD30 have issues but i suppose it ends up coming down to your maintenance and modifications done to ensure the longevity of the engine. There are some mighty rigs out there with the 3 liter, and some great ones with the 4.2 also, so don't worry about the saying "There's no replacement for displacement" and choose what you believe will take you places that you want to go. Cheers.