For beginners I usually recommend a plastic tank. Yes they are light and yes they will "float" over obstacles rather than soak up the bumps in the suspension, but at the price it is very nice. The plastic ones are a bit easier to modify as others mentioned, but as all of Taigen's tanks have plastic upper hulls that point can't be used in a metal vs plastic for us. The lower chassis is a whole different story though. A metal lower chassis will provide less flex all while strengthening the lower hull at the same time. It of course can be used for a bit more rougher outside work, and still gives you the best of both worlds as it will be an aluminum tub with a plastic tub around it. This will allow you to modify the outsides as a plastic tank and still keep the strength of the metal. The new Sherman is a whole different story as the lower chassis is a solid 2.2mm thick the whole way through. This chassis is a lot easier to waterproof as there is very little entries for water or suspension holes.

My favorite mix is a metal hull, steel gearboxes, metal drive and idler wheels, plastic tracks, and plastic road wheels. Of course everyone has their own mix/match but once again the end purpose of the tank will make a large determining factor on what you should equip it with. I will say if you do plan on getting into the hobby even half way serious then go ahead and get a metal chassis. From there you can work your way up to what you want. A good example is our Tiger 1 plastic model, it comes with a metal chassis and a torsion bar suspension but comes with all the plastic components so you can upgrade as you wish. Please let me know if you have any specific questions about the models, I have been AFK for the last week or so with a show and trying to catch up to everyone, but you can always catch me at my number in my signature. Just make sure to ask for Erik!