The more flavor options, the more likely I am to buy from them. That being said, this can be deceiving. I've tried vendors with less choices who have been waaaaay better than those with tons of choices. It's hit or miss and the only way to know is to try. I usually only order from those who sell reasonably priced sample packs, that way I can try lots of flavors and not feel too cheated if I hate their product. So far I have tried:
Dragonfly - not bad. This was the first vendor I ordered from (and where I got my first ecig, a 510). I don't think I'd order theirs again though unless I was completely out and was placing an order with them for attys or something. ($10 for 10ml or $19 for 30ml + Shipping)
Juicy Vapor - Huge selection and you can mix your own, however, they are lacking in the flavor department. The flavors are weak and some have a very strange chemical/perfume quality. I did enjoy Tiger's Blood, Chocolate Irish Cream with Mint and Raspberry Margarita. ($44 for 10 - 6ml sample pack + shipping)
Rockstar Vapor - I really like these. The grape and watermelon were more like jolly ranchers than fruit, but the quality is really good. I like the Strawberry Waffle the best. A little on the thick side but they have awesome blue glass dropper bottles and they ship EXTREMELY fast. (~$25 for 5 - 15ml including shipping)
Want2Vape - These are great. Awesome flavor but minimal selection. They have a lot of tobacco/cigar flavors. I've like all the ones I've tried so far (Campfire Coffee, RY4 and Creme Brulee). Would definitely order from them again. ($18 for 10 - 3ml sample pack +3ml atty refresher, free shipping)
I have orders coming from Kick Bass Vapor and Bombay Vapor also.