I went with price per ml delivered. I also looked for samplers since they sold in smaller sizes for somewhat smaller cost. First off, I gotta say that many say it is hard to find juices that they would consider all day vapes (ADV). For me, it was about 10%. I had some success with VapeWild. Mt. Baker Vapor (MBV), too.
When I traveled by myself, I would take a couple of hours and sit in a vape shop that had shop made juices and internet available juices. I would sit and try a lot. I would buy one or two of the local, but I would take note of the flavors that I liked and that were available on the internet. The internet is just cheaper. That would cut costs a little.
I used a spreadsheet to track what I tried, good or bad. Slowly, I found juices that I rather liked. But, it was never from the same vendor. But if I did order that good flavor on the internet, I would try a couple of others from the same vendor. I didn't really like buying a single juice and paying full price for shipping. So, I would try a couple of others.
A really slow process.
Now, I just DIY. I still write a lot of notes so I remember what I have been doing with the recipe to make it. I enjoy it more and the costs are lower in the end.
Good luck!
I don't want to buy a 15ml bottle of a juice I've never tried. 
