(You can just write in english, since we do understand it.)
I'm not sure is there 'the most popular class'', if you want to do an easy build, then go for short course, all you need is a car, paddles and nice motor/esc, etc.
In modified you can drive with a short course truck (see above), or buy a Axial AX10 and drive with it, it has been proven to be quite good (as far as i know).
Im not sure about your sentence wether do you like or dis-like 1/8, I believe its the most expensive, and free class, there you can build pretty much the whole car yourself.
Make sure you have a proper driving area nearby before making a Foff car, since paddles only work well on sand and snow.