Till date, I have installed only two desktop wallets for altcoins - these are Byteball and Deep Onion. A few months back, I sold all my Byteball and removed the wallet from my system. But I am still holding some Deep Onion.

If you are gonna hold coin for long term then i suggest you please hold it in wallet. cause you don't know about any exchanges. you don't know they are gonna stay or scam. yes there are many exchanges that they provide us great service from couple of years. but we also see many exchanges that they scam many people and project. so my opinion is wallet. but if you are a regular trader than exchange is the good option too. 

On the exchanger, the coin storage is very convenient, you can quickly sell or exchange them for others. But it's safer to keep it in your wallet.

no way , dont use for holding exchange! Have bad opinion! use only wallet, better what  to use wallet, which downloaded on your computer

In cryptocurrency, there is not the safest way to keep the currency.
1- cold wallet (the most secure that exists). They are called so: Lenger nano s, Trezor.
2 - Coin Purse for ETH-based coins - Myetherwallet
3- At the stock exchange, I would not advise you to keep your coins. But I do it myself

I think  wallet is better than exchange for long-term holding.   Exchanges are always the target of hackers. It is not safe. But if you want to trade you must hold your coins in Exchanges. You must determine your gold, holding or trading?

You should always keep your cryptocurrencies in your wallet.  Only keep coins on exchanges for trading purposes.  With the recent hacks of Coincheck and Bitgrail, it should be a message that exchanges are not safe for storing coins.

I think to keep coins on some Exchange site isn’t good idea. Use wallets for each coin and HOLD.

both have the same risk. I've had phishing on the wallet, and at that time I believe that the asset store on the exchanger is better. until I also experienced the theft of assets on the exchanger. I no longer trust in both

I want to answer this question by another clear question that will help you to catch your answer. please answer this question and think about it: "can you put your assets in my wallet?" maybe you answer "No". that is true, when you have money; you only hold your assets in your wallet. so exchanges only places for changing and not for holding