keeping tokens/coins in exchange are too risky, but if you use the exchange just to sell your token in just maximum of 1 month, it is not because keeping them for a long term can cause of loses or in some case (knock on wood) sites can be hacked. so i suggest you to keep your tokens/coins on its designated wallets for more security purposes.

The question is really very important, because a lot of people, for some reason prefer to use exchange wallets, but I use both of them, because there are all kinds of situations, so I use both options

Keep all coins online is dangerous. Even the most trusted exchanges can be hacked or closed. If you are an active trader, keep the needed amount at the exchange, but all "inactive" coins should be at wallet.

Both are advantage and disadvantages to keep the coins holding. Suppose you hold coins on the online exchange and that was hacked by the hacker then no body have any solution to recover the investment. if you keep your coins in offline wallet and due to any reason you lost your wallet or its data and can not recover from any where then this is also loss. In this case online wallet is best but in that case hacked by hacker then offline wallet is best. Now your choice is depend on you.   

if you will not exchange your altcoin with local money or trade it, you should keep it in your wallet to avoid something you do not want. but if you are a trader, it is quicker and simpler to keep it in exchange.

I would say a bit of both. Organize your coins and tokens into many different wallets and exchanges with amounts you are willing to lose if things get compromised. By doing that, even if some wallet/exchange gets hacked, your loses will be minimal. Sure, it takes a lot of work to get everything up and running, but better safe than sorry and most importantly, you will be flexible. Imagine a coin that hits all time high and stays there only for a couple of hours. If you would have a coin like that in your wallet and the network is clogged, you wouldn't have time to send it to you exchange. By having different coins on exchanges you can avoid that risk. Search for top wallets/exchanges for different coins and allocate them there. At least, this is what I would do and I'm not saying my advice is better then anyone else's. At the end it's up to you.

I agree with you. Exchange - this is not a place to store coins for a long time. This place is only for trade. If you withdraw money to your wallet, it will reduce the risk of losing money.

Exchange is good but Wallet is more safe as Exchange. wallet with private key for coins that you dedicate hold for long term investment.
Remember not all of the wallets are fully secure too, Just try to consider how security measures already applied to those purses.
I use exchanger and 2fa for trading. thanks.

I would choose wallet over exchange because it's easier to manage the money using wallet. It is also more convenient transfering money or transacting with others using the wallet.

It all depends on your choice and what you intend to do if you want to go into trading the exchange site is the place your coin should be and if you want to hold then you can hold your coin in a wallet of your choice. Different options for different purposes that is how it is.