for me, its Caramel Tobacco or Robacco, both from bluemistvaping.com I definitely switch it up throughout the day, and from day to day, so these aren't true "all days." But, most days I vape mostly CT or Robacco.
Like others have said, it is a very subjective thing. the only way to find yours is to keep trying new juice until one really sticks. even then, keep looking for another couple of flavors that you really like, because tastes change, and its good to always know you have something that will satisfy. Sometimes i need to lay off of my favorites for a day or two, to let my taste buds "reset."
As others mentioned, samplers are a great way to try lots of flavors without breaking the bank or ending up with tons of juice you don't care to vape. Bluemistvaping.com offers 5 packs of 3ml samplers for $10. Personally, i rarely order from anyone else anymore. I do still try out new vendors, or juices that have been highly recommended, but after trying so many mediocre juices before finding bluemist, its nice to be able to order from one vendor and know that i will be happy with the juice. Not to mention, their prices are pretty much unbeatable. $10 for 30ml? $30 for 180ml? Mixed to order in the U.S. by good people who provide great customer service. Probably half of my posts on the forums are me recommending bluemist.
You can check out
my reviews of Caramel Tobacco, and of a few other bluemist flavors, if you're interested.