Who do I practice Smash Ultimate with?

I'm going to get comfortable with all the movements/attacks/tricks/ect. in practice mode first, then move onto beating up the AI. As someone who wants to get serious with Smash, who should I practice these things with?

I think I should use a character that has decent attacks of all types and direction and decent movement, so that I can translate the skills to one character I choose to get good with. For example, I dislike Mario for this because his down-B isn't a damaging move, so I've been using Kirby. What other characters would you recommend I do this with (and how else do you think I could improve this practicing method)?