Although any bit of oil that dribbles around should be a little better, unless you are going radical, I just haven't seen flat tappet failures, solid or otherwise, after a good break in and good oil. Admittedly, I run street lobes up to only about .600 lift, but I never think twice about them to tell you the truth
The absolute majority of the oil comes from the crank, so keeping idle on the higher side of what you like, running the right oil, correct spring pressure, and making sure the lifters are free to rotate and no binding in the valve train are the real must-dos.
As far as brands, I have a set of new Morels dumbells that are very pretty here, and likely leftover if you are in a bind. However, I have bought bulk "Johnsons" off Ebay and they worked great on a 282S, who knows what they really were LOL In the end, I think your oil and assembly will be the key factors