Remember the next bull market is caused by Bitcoin's halving, so it's 100% Bitcoin price will get impact while the other altcoins are just following the market, it means there's a chance some altcoins price will not increase.
Low cap altcoins is the best choice if someone want to get rich quick by taking risk losing all of your money, while Bitcoin is slowly and keep rising, but it's the safest coin.
If bitcoin will rise again after the halving, as it was in the previous cycles, then altcoins will also rise, because the price of altcoins is measured not only in dollars, but also in bitcoin. Another thing is that if you buy bitcoin, it will probably be more profitable than altcoins, because altcoins are roulette. If you are lucky, you will get a huge profit, but if you are unlucky, you will lose money.