I had my kitchen renovated a few years ago. I had an undermounted single basin stainless steel sink installed. It allows for your counter to be the star of your kitchen; easy to clean. You have a flat surface to take a wet sponge and swipe crumbs from the counter into the sink. I am quite happy with my sink!

You want an undermounted sink with a slight positive reveal. No hump to catch crud like the top mount.

I asked this question because someone said they had a mild problem with their undermount sink. And I've also saw mold on undermount bathroom sinks at businesses. Maybe by they just didn't clean them IDK. It was actually the places that sell the countertops .

I've had a drop in then with remodel went with the popular undermount but we are getting ready to build a new home and I'm seriously considering the drop in again due to the cleaning between the sink and the counter top, it gets moldy even though it has a sealant around it.

If you request a positive reveal your sink will have a small ledge so the counter won't overhang the sink. The gunk collects with larger negative reveals.

I never have mold or any issues with my undermounted sink. I do clean my sink daily with Softscrub: takes one minute.

"I'm seriously considering the drop in again due to the cleaning between the sink and the counter top, it gets moldy even though it has a sealant around it."

If there is black/brown mold at your undermounted sink, it's because your sink is leaking. Not drip-type leaking, but capillary action type leaking. The tiny gap between the sink flange and the stone bottom is sucking in dirty sink water.

You cannot topically caulk your way out of this. The sink must be dropped, the flange and stone bottom cleaned and resiliconed, the clips abandoned, and the sink strapped in place. That fix is permanent.

Black/brown crud is no reason to get a top mount sink.