I happen to have a bunch of kits ATM. (Hagen, Tetra, Wardley and API) I can't really say I have a preference for any of them. One general complaint I have is with pH kits, they all have seem give me the same trouble distinguishing different shades of green or blue. Wide range tests are particulary difficult for me to pin down accurately. I find the narrower the range, the easier to get a more accurate read. I have a Hagen 6.0 to 7.6 kit that seems pretty good, I'm able to distinguish right down to + or - 0.1 A while back I used all 4 pH kits I have to see if there was much difference in readings. I found no real difference.