I use Clip Studio. Pretty good price point for all the tools I really want, though admittedly it is the only tool I've bought so I don't really have much room for comparison. I suppose Medibang Paint could work as a plausible free alternative.
That being said, you say that you're at a basic level, so I think it would be preferable for you to focus more on just practicing as much as possible with whatever you have. Including, as @keii4ii mentioned, pencil and paper.
At this point, Experience > Tools