I personally prefer storing my long term investment in my personal hard wallet because I find it safer. Putting your eggs in one basket would be a lot risky since hacking is everywhere and that could possibly happen even in highly reputable top exchanges. Store funds in exchanges for a short-term period and trading purposes only and make sure to keep your long-term investment in a more secured wallet where hacking isn't possible.
Exchanges are recommendable mainly for trading and they serves their purpose perfectly. There are various or numerous wallets, I use Binance which happens to be one of the most safest exchange in the space and difficult for some scammers to invade one's account, the only way that could happen is through phishing of spammed mails. Exchanges are used for trading but some traders and investors also stored their long term coins with exchanges favorable to them. I rather have my long term investment in a separate wallet like Trust wallet which only me can assess it with my 12 coded phrases.