Tips and Tricks
Increases your attack damage. Every upgrade of your attack, the number of hits you attack a single enemy will be lesser. Aim for single hit for every enemies except bosses. So increase your attack as soon as possible to be able to farm coins easily and get experience very fast.
Critical amplifies your output damage at a certain rate of chance. Critical still depends on your "Attack" so to save money, avoid upgrading your critical and invest only in "Attack".
Decreases the damage you will take from the enemies. This is your most important stat upgrades when you are at a more difficult stages/level.
Your primary purpose for speed is when you have enough ATTACK and DEFENSE to grind at any levels. Increasing speed will increase your kill over time ratio, so you can get more coins and exp at very fast rate.