I did a poll recently...
Salifert and Hanna are in a close race... Lots of folks mix and match
Red Sea is third but that doesn't make it any less.
It really comes down to preference I use both Salifert and Hanna. Salifert is probably the most popular brand most folks I've talked with are using or have used Salifert at one point or another, they are relatively accurate testing kits. Hanna Instruments make great accurate products as well but you have to buy reagents that are not cheap and the kits themselves are expensive.
I think different manufacturers might be best. See the brs video series. One is below. I personally use Hanna for alkalinity , copper, ulr phosphorous. Salifert for mag, calcium, nitrate.
Learn More Hanna Instruments dKH Alkalinity Checker Instant digital readout The device that changed the lives of SPS hobbyists forever! The dKH Checker produces an accurate digital readout
I would stick with salifert and Red Sea, most are cheap enough to try each and see what you prefer, some people can read a pink shade better than a yellow, so it’s down to preference, the only salifert I would recommend not getting is the ammonia, go Red Sea for that.
I use Milwaukee for salinity, Hanna for calcium, alkalinity, phosphates, ph and nitrites, Red Sea for nitrates and ammonia, salifert for magnesium and iodine.
i use a combination of red sea for checking (ammonia nitrates occasionally) calcium, red sea pro for nitrates phosphates, and hanna for alk, phosphates (u.l.r.), and calcium.