I would like to start daytrading altcoins, but I need to know which ones are best to work with.
To get started choose a good exchange like
Binance,
Kucoin or
Coinbase.
You need to learn? Then I recommend some good courses:
https://academy.100xcoin.io/It is also necessary to know that you should not use money that you are going to need, the bad days are many at first, but do not get carried away by emotions, you must be a cold head for these things.