Two different vehicles for two different uses. For offroad hands down I'd take the Tundra, for pulling a heavy load hands down the Ram diesel.
I had a 2006 ram 2500 diesel, it was a great truck and I still wish I had it. The downsides are, it is heavy and front heavy so not a great offroad truck. The dodge front ends will need a rebuild at ~100k miles and that will set you back $2-3k depending on the shop. Used trucks have great resale which means for a '10-14 you might as well buy a new one especially when you factor in possible repair costs. If you do buy used, don't get one that somebody has chipped as you could be looking at expensive engine and drive train repairs.
For towing any appreciable load the diesel is the way to go. The torque makes pulling a load a joy, and the added weight and stiffness of the suspension of the truck gives you control over the load vs. the load controlling you. The downside is such trucks are not as enjoyable driving unloaded.
