The 3 main 3D software programs generally used for Content Creating for Trainz are GMax, 3DS Max and Blender, not in any particular order. Except, 3DS Max is VERY costly, unless one is a student and get 3DS Max through your school. But there are limitations with its use this way.
Easy of use is different for different people, none of the above programs are easy to use. One needs to stay and persist with the 3D program one chooses to go with. Once this is somewhat mastered, the world is your oyster creating wise.
I use 3DS Max, I use it for about 6 years now and check my signature pic below, this is what I can do now after starting with very simple objects, progressing as my skills increased to more complex objects, animations etc. Age is no barrier to learn a 3D software program, I am now 72 years young and there are some people here who are retired or whatever and do some content creating for Trainz.
Cheers
VinnyBarb