Wizard Labs - for 85% of the flavorings I use (ones made by TFA, CAP, FA, FW, etc). IMO, they have a huge variety of flavorings, super prices, top-notch packaging for shipment, and wonderful Customer Service.
One Stop DIY Shop - for the other 15%, which is for their own proprietary One Stop Blends and One Stop Flavors. They're absolutely wonderful! (My personal favorites are Lucky Shot, Baked Cinnamon Roll, and Lotta Latte). You just add 8-12% of a single one of them (% to suit your own taste)...to your PG, VG, and Nic Base, and it's good to go! They also carry flavorings from TFA and others, but not as large of a variety as Wizard Labs does. When I order from OSDIY I may toss in a few TFA or others that I need, too, while I'm there. They also have terrific prices, wonderful customer service, and very safe packaging for shipment.
Have never had any damage in shipment, a mistake or a shortage on an order, or other problems from either of the above places! They'll always get my DIY business.