When I first started drinking coffee, I had to pour the sugar in because it was SO bitter. Of course this was military grade coffee which means it could also be used as turpentine!
Now I buy quality coffee that does not need any thing added.
If I am having a straight espresso I will add a little sugar. For any other coffee drink I never add sugar. I love cafe au lait and when you froth milk there is enough of a subtle sweetness that sugar is unnecessary.
I prefer no sugar in my coffee but at the end of the day I guess it's all preference. If you like a lot of sugar in your coffee go for it. Whatever floats your boat
I am modifying my previous answer. I no longer add sugar to my coffee, no matter how I drink it. I like the taste of coffee unadulterated. So I've been drinking my espresso straight lately. The only thing I'll add to coffee is milk.