Well I'm sure you'll get a ton of different replies, as
juice vendors and flavors are a matter of taste, however I'll shoot out some of the ones I've used and had good results from. YMMV.
AVE (Alien Visions)-great VG juice
KBV (Kickbass)-good all around
BWB (Backwoods Brew)-great tobaccos
VaporBomb-lots customization options
FSUSA-tons of flavors, surprisingly good for a site that does a lot of hardware too
TVR (The Vapor Room)-not the greatest selection but some really good tasting juices
Honeyville
vaping-like TVR not the greatest selection but some delicious offerings
Mrs. T's Bakery-great juices if you have a sweet tooth
As far as flavors go, everyone's taste is different, however I will guide you away from any juices that are flavored to mimic meats. Unless you really want an "adventure" avoid anything labeled Crab Juice, Bacon, or BBQ Ribs; really there's no way to describe the horror that will befall your taste buds should you attempt to vape any of these.
Best advice is to pick up samples (3-5ml sizes) from a number of vendors in a myriad of flavors. Just remember not to go too large a bottle to start out with, your sense of taste can/will change as your taste buds repair.