FlavourArt (FA) and Inawera (INW) are probably the best; The Flavor Apprentice (TFA) and Cappella (CAP) next best, though I won't use any other cream flavor than Cappella's Sweet Cream -- it's spot-on authentic, AND diketone-free -- I keep 2 diff bottles in use, one without the dripper tip for mixing, and one with, for adding drops to food, it's so absolutely realistic -- makes a terrific addition to a low-fat diet! Molinberry's Glamour Chocolate is the only chocolate flavor I use, because it's the only one I've been able to taste -- some people seem to have tastebud-blindspots for certain flavors. There are a lot of other brands, but I've either never tried any of their flavors, or wasn't too impressed with what I did try.
FA also makes some outstanding additives, for flavor-shaping.... Flash, which increases throat hit; Bitter Wizard is great to add to tobacco vapes, to remove the inherent sweetness of VG. The best sucralose I've tried is definitely TFA; I dunno what they do to it, but it doesn't have that artificial whang as some other brands of sucralose have. FA's MTS Wizard seems to help with smoothness; TFA's Koolada gives a cool sensation without the icky taste of menthol. Acetyl Pyrazine is the basis of most nutty flavors, and is good in "bready/cakey" type flavors, or tobacco flavors, but it's really strong; smells just like Fritos, and if used too heavily, tastes like sweat socks.
If I want some of that sort of flavor in a vape, I generally prefer to use TFA's DX (diketone-free) Hazelnut; it doesn't taste extremely like hazelnuts, but the AP component is great deal more subtle, not over-the-top "fritos flavor". Ethyl maltol is sometimes used as a mild sweetener, but apparently it's more valuable to enhance the "feel" of a vape, gives more richness than merely sweetness. For that, I usually just use TFA's Cotton Candy flavor -- Cotton Candy is just ethyl maltol in a 10% concentration; using the TFA Cotton Candy flavor maintains uniformity and repeatability.
Andria