Is their a juice manufacturer that is known as the "safest" and does not include ingredients that may cause cancer?
I don't know of one that is the "safest". However, you can check to see if any ingredients that some people try to avoid are in their e-liquids...
if the website lists all the ingredients of each of their juices.
These ingredients are considered by most to be OK,
from what I've read & heard: Natural & Artificial Flavors, PG, VG, Water, Tricetin, Sucralose, and Ethyl Alcohol. (Some people like to avoid the Ethyl Alcohol though, because it's essentially grain alcohol, and gives a sort of "sting" or "bite" to some flavors if there's too much in it.)
Ingredients/words to look for that some people consider to be
not OK, again only as far as I can tell: sometimes it will just say "diketones", and other times it will list them as Acetoin and/or Acetyl Propionyl.
If you're in doubt that an e-liquid contains the above, maybe because there's no detailed ingredient list given on their website...give them a call and ask if you're really concerned about it.
I, personally, still buy several flavorings to make my own e-liquid that contain Acetoin and Acetyl Propionyl, but only if there is no alternative of the same flavor that doesn't contain them. Most websites will show the ones
without those as having a DX designation in their names (ie. The Flavor Apprentice flavoring named DX Bavarian Cream is the alternative for Bavarian Cream that has no diketones...the Acetoin nor Acetyl Propionyl).