T19P = Pre Raid Gear
T19H = Heroic Raid Gear
T19M = Mythic Raid Gear
Keep in mind they are not updated at the same time, so check the date especially cross spec. There are still huge swings from update to update.
In my opinion T19P is the most valuable at the moment as it shows the standings before progressing, T19M basically shows the standings AFTER progress where DPS doesn't really matter that much until the next content is out.