Which is better: Invest my Bitcoin on legit mining sites and purchased power before the halving because it is currently cheap or save my bitcoin and trade it after the halving because its value might be doubled?
Better purchase bitcoin during halving and go trading, than investing it on mining site. You can gain high in trading 5% to 10% per day gain is good.
entering trading without experience means losing -5% to -10% per day instead, trading is a good way of making profit but it needs some expertise because it is a hard thing to do.
it's why a new user without experience in trading is just required a low amount to do that. if it's only a little amount you will not worried if anytime you get a losing every day until that amount is empty. and after you have some experience in trading you can starting again with more amount to get back your losing amount.