I am getting top mount simply because I have read that the caulk/seal is harder to keep clean on the undermount.
I think if you dry and rinse regularly, neither are a problem. Wet = mold and it can happen regardless of how it is mounted.
My DH does not regularly clean and wipe the sink area, so for sanity's sake, the top mount will be easier to use a bleach stick if I need it and to have it air dry faster.
It is my preference.

Our top-mount Kohler sink of 20 years has no crud or gunk growing next to it. After it was installed, I filled in a few places with a clear silicone caulk, and it has been great ever since. I keep an eye on it, etc. My sister has an undermount Kohler, I don't know how old it is, and I can see the black crud growing down from the negative reveal. Grossssss.......

Any ideas on the sealant being applied under the rim of the top mount sink instead of at the outer join between the sink and counter top?

That's interesting to know paulflyboy.

I guess the question running through my mind is how my parents' sink ended up with no seem visible anywhere...no matter how small...since it's actually underneath the rim of the counter and not where the two surfaces meet.

I'm just wondering why this isn't the standard for installing a top mount sink?

The industry standard for sealing a topmount sink has always been plumber's putty. It is superior to silicone in most respects for that use. You just roll out a rope of it, place it under the rim of the sink, drop the sink in, tighten the clips, and then remove the excess putty that is squished out. Simple, and plumbers putty never hardens so always maintains a seal if you've used enough of it. It is NOT advisable to use it with natural stone as it's oil based and the porous stone can pull the oils out of it and become stained.

That's great information, thanks live_wire_oak! I didn't even know the name of it until you told me :)

Well I will be using CaesarStone counters, so is it applicable for me?

Is there still a danger of dirt getting trapped between the sink rim and the counter? Tiny particles of dirty would logically get in somehow but looking at my parents' sink I just don't know how it stays so clean!

What if you want to change the sink in the future? How do you remove it later on?

As LWO said, plumbers putty never hardens . You just remove any clips underneath, perhaps stick a putty knife under the seam, and pry/lift it up.

Hmm, just found some information elsewhere on the Internet that apparently Blanco advise against using plumber's putty on their Silgranit sinks.

I guess that explains why it always seems to be silicone then.

Thanks for this info! My husband and I just set our first drop-in sink (an old farm house cast iron enamel sink). We put new quartz countertops in and found some non-oil based plumber’s putty. We had a small mishap on our first attempt, but since it was plumber’s putty, we were able to retry and reset! It worked great!

• Oatey's Stain Free Plumber's Putty is one brand. "For use on granite, marble, quartz sandstone and other materials."

Yes! That is the brand we used.

I don't recommend plumber's putty. I've heard the EPA made them take out the chemical that kept it soft. When it dries eventually, it leaks. I've pulled hundreds of leaking disposal flanges that were set with PP. 100% silicone now.