you're welcome in advance.
I don't think ATB is a brand, I think it's All Terrain Bike, or mountainbike. For a while now, most ATBs and road bikes alike use near-identical 31.8mm stems, which is handy because they are interchangeable.
The most important thing about a stem is to get one with the correct length and angle to achieve your desired fit. What don't you like about your current stem, what's driving this need to change?