I don't want excessive borate, which leaves out Seachem.
I don't want vitamins or anything else organic in my mix (because I doubt their utility, they degrade with time to who knows what, bacteria may thrive on them as I store new salt water for a substantial period, they are totally undescribed with respect to amounts or identity, they are often not naturally present in natural seawater at appreciable levels, and because I've occasionally had them mess with my skimmer), so that tosses out some like Reef Crystals, hW Marinemix Plus BioElements, Kent, Coralife, and Nutri-SeaWater.
I don't want excessive calcium (long term use of limewater as I use drives up calcium, so I do not want it starting high), so that tosses out a bunch, such as Kent, Seachem, Coralife and Oceanic.
I won't use certain lines of natural seawater due to excessive metals in it.
That only leaves a few to choose from, such as Instant Ocean and Tropic Marin Pro.