i tried to feel out the crowd myself a few months ago on this for immersion coatings...
thread332-344253
My gut feeling is that zinc primer and epoxy primer systems both work fine, all other things being equal. Regardless, there are enough tanks out there for both to say that zinc-epoxy-epoxy and epoxy-epoxy-epoxy are both the "Standard" system you asked about. unless you go down the path of extending coating life with plural-components, the tank will be getting recoated in the next 10-15 yrs anyway.
If you want the same system for multiple manufacturers for bid purposes, pick a 3-coat epoxy system since everyone has it. If there is preference for zinc primers by the owner (i'm going to go on a limb and assume you aren't die-hard entrenched in one or the other), exclude the non-player manufacturers. If there is no preference either way, list all the approved manufacturers and let the contractor choose the system. the owner will likely have a preference to few certain name brands already.
if these are new tanks, look into having the plate metal shop primed except weld heat zones... you'll cut down on surface prep in the field and probably get a better prime.
my $0.02. i hear a lot of opinions about those primers but i just don't see many case studies or hear stories about how well or poorly "that zinc coated tank" is doing.