An under-sink unit typically requires another hole to be drilled and another spigot, right? Something of a hassle with a stone counter :-/
I had a whole-house coconut-shell-carbon filter at my old place. Did a great job of filtering HS out of the well water, but needed periodic replacement. I'm on city water now, which smells like ass. There's a small filter inside my fridge, but the tap is also inside, not on the door, which makes it rather inconvenient. I'm tempted to have bottled stuff delivered so I can have a crock dispenser in my office -- I telecommute and for medical reasons need to drink copious amounts of water.