Start with the weapon, not the stats
The first character you unlock usually comes with a fixed starting weapon. That weapon carries your damage for the first few levels.
A weak opening weapon means you scrape by until a lucky gem drop saves you. A strong one lets you focus on learning.
What a good starter gives you
A starter worth picking does two things. It clears the early waves without help. It also scales well enough to stay useful past the halfway point.
Some starters trade damage for speed or area. Early on, damage matters more than movement, because dead enemies cannot catch you.
The safe first pick
Pick the starter whose weapon hits multiple enemies at once. Spread damage keeps the screen clear while you figure out the upgrade menu.
Once you have a few runs under your belt, switch to a starter that forces a different playstyle. The weapon priority page explains which weapons pair well.
Next: How leveling and gems work.