Different chocolates are made with different amounts of cocoa solids. Generally, cocoa is the most expensive ingredient, so some manufacturers will try and bulk out the chocolate with more sugar (and for milk chocolates more milk powder).
The best way to tell the quality level of a chocolate is to look at the % cocoa solids claimed on the packaging. Generally the higher the number the better the quality.
Although, once you go above 70% cocoa solids, there is less sugar to balance the bitterness of the cocoa so you may find it too intense. It’s a matter of personal preference. I know people who swear by 99% cocoa chocolate which is pretty much sugar free. Personally I like something a bit less austere and tend to enjoy my chocolate in the 65-70% cocoa solids range.
Why not buy a few different chocolates and have your own tasting to figure out what works best for you and your guests?
