There are many good flavorings by different companies, but I usually stick to The Flavor Apprentice (TFA) and Capellas (CAP). I will list some of my favorites below.
Capellas
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Vanilla Custard v2
Sweet Strawberry
Sweet Cream
Marshmallow
New York Cheesecake
Vanilla Cupcake v2
French Vanilla v2
Butter
Flavor Apprentice
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Berry Crunch
Fruit Circles
Brown Sugar Extra
Ripe Strawberry
Dragonfruit
Dx Banana Cream
Ethyl Maltol
Malted Milk
These are just a tiny subset of the flavors available. Also, many people seem to enjoy FlavourArt as well, but I have never tried them. I would stay away from Hangsen, as they are a Chinese company and you don't know what kind of crap they are putting into their flavorings.