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?
Ok, well I do not advise buying mining gear until you can fully understand what numbers like difficulty and price we will be dealing with as well as there will be a lot of hardware for sale after the halving I imagine. I'm waiting for those things also. It's tough to say whether you should sell before or after the halving as it is unclear what will happen on the day of it. Could go either way.