I quite buying any chocolate which doesn't state the cacao percentage on the label some time ago--and have been lobbying the FDA to make such labeling a requirement.
I settled on the Ghirardelli 72% chips a couple years ago as my optimal balance between quality, flavor and cost--chips are always considerably less expensive than bar candy.
I sit with a bag of the 60% cacao bittersweet on my desk as I write. I was forced to switch to this from the 72% when it became impossible to find the 72% locally (on my income, price is always important!)
These are smooth, melt evenly and have a nice chocolate flavor without any significant other notes I can detect (your tastes may vary!)
Americans have a problem with 'bitter' flavors--few US dishes use the bitter taste at all, and most Americans seem to feel that bitter equates to bad. Well, unsweetened cocoa is bitter, and it stays that way until you get to a fairly high level of added sweet.
This means that high cocoa content chocolate is a taste that must be cultivated to some extent--how many coffee drinkers out there truly enjoyed their first cup? (Regular drinkers are addicted...enjoyment may come second to getting their fix.)
My cookie recipe is based upon the Joy Of Cooking recipe, which I double everything EXCEPT the chocolate ships, and add 1/8 tsp red pepper (ground) and 1/4 tsp orange or lemon extract. These chips work quite well (though short of burning them, it's pretty hard to make a chocolate based dessert which I'd not eat...I even carried the infamous 'desert bars' for a few months in my car--slightly chocolate flavored wax is better than no chocolate at all....)
For several months I went through 4-5 bags of these a week as snacks.
The best chocolate is the one you personally like best. After that, it comes down to the recipe it is being used to make.
These are better than average bittersweet chips which can be found in grocery stores at a considerable savings compared with any online vendor I've managed to find.