Oceanic is my new salt of choice. It dissolves quickly, and is well balanced in my opinion. I don't have a Magnesium test kit, but all of the readings I've done on Oceanic mixtures are practically identical to the results posted by ReefNut.
I used to use Instant Ocean, where I would have to mix the salt overnight to get an accurate reading for salinity. The first time I mixed Oceanic salt, the salinity read 33ppt on my refractometer two minutes after adding it to RO/DI. I waited overnight to see if any more salt dissolved to bring it closer to my goal of 35ppt. To my amazement, the refractometer still read 33ppt! A little more salt, a few minutes wait, and the salinity was right at 35ppt.