Most flavors I would say FlavourArt. This
guide has some great info and
reviews about most of the flavors. It's not a question that can easily be answered with a simple "this one".

I like a few of LorAnn's flavors but not too many. There are many FA flavors I really like.
You can
buy 3ml FlavourArt from Nikhil and dram sized LorAnn can be bought pretty cheap on eBay.
What flavors are you wanting to mix? It helps to narrow it down some then we can give you our opinions on those flavors. Welcome to DIY, you'll have a lot of fun, just be sure to read, read, read.