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Since we have the higher percentage chance for the to move upwards because of the increasing demand, sure you will earn more money longing with 3x leverage and your risk level is low with 3x leverage on Bitcoin with €100 , but to me the best way to go about this, is trading Bitcoin to get more BTC , this way your are holding Bitcoin and profit will be in BTC, that is you not just only gain from your €100 worth of Bitcoin and have it increased but also your profit increases as the value of BTC increase.
If OP has time and active with the market can go to the futures with just low leverage but again there's a fee on it in too much holding your position of course, but if OP doesn't have any time to watch all day the market like we are seeing right now the market is going into a bull run movement he can make a hold until the next all-time high. Futures still take a basic understanding and knowledge to make a trade with the help of technical indicators and technical analysis as a guide for your position. Always use the basic TP/SL as your security to yourself to prevent burn your asset.