Yes, I know hardware wallets are the safest options, "not your keys not your coins" etc...
Hardware wallet is one of the safest, there are other safest wallets. Paper wallet is also safest, using airgapped device is also safest, multisig wallet can even be one of the safest in some cases, using electrum in cold form and one as watch-only is also safest. But, know that not you key not your coin still also applied to all noncustodial wallets, but the reputed ones are recommended.
But if I'll leave some coins in a "software", what is the safest option? Leave it in an exchange like Binance or trust a hot wallet like Samourai?
Not you key not you coin rule still applies here. Binance will not give you private key, which means binance will have the private key, which means binance have the full control over the coins you have with them as they are the one that will unlock the bitcoin on blockchain, you have no full control as it is not your coin on blockchain.
Exchanges are often hacked, because they are often targeted by hackers because of high amount of funds they are controlling.
The reason I'm skeptical about about other software wallets like Exodus/Samourai etc is because I'll have to trust that their software wont be hacked, nor my mobile phone. While in Binance/other exchanges, they have a whole team dedicated to that.
A malware that can hack your wallet can also easily hack you exchange account, but it is you that will have to learn ways to avoid your wallet being hacked.
Why is it harder to hack/attack a software/hot wallet than it is to hack Binance/exchanges?
Exchanges have so much funds with them, they are hackers target. Unlike noncustodial wallets that are hold by individual, any individual that do not also protect his wallet can result to hacked wallet. Also, exchanges are making use of hot wallets for storage.