oh, try to make some capital and resell items

Texturing=high input/high output. It requires the most effort, so not the easiest. However, I'd say it's the most rewarding, if only for the satisfaction that comes from completing something.

For betting and item trading, you'd need to make an initial investment though. And the easiest way to get that would be buying tcs.

Buying tc or a booster is the easiest way to get tc if you are able to purchase it. Making good textures that will make a lot of tc can be a hard thing to do unless you already have good art skills with photoshop or gimp etc.