I would say equal to any other elf, perhaps slightly more acute? I'm not sure if the living in darkness thing would really affect their other senses; after all, they can still see in darkness, so it's not like they have to make up for the lack of other senses. They still get the Spot, Listen, Search affinity as a regular elf. Though these senses are somewhat dulled in Light Sensitivity, I can't imagine why daylight would affect a Drow's sense of smell, other than an unfamiliarity with day-time smells, which would be at the discretion of the player. However, I could see smell being stronger in Drow because of their constant need to be aware of poisoned food and drink in their society.
Getting technical,
Keen Sense might not mean Elves hear better than other humanoids, but instead more readily pick up on what their senses are telling them. They're treated as actively searching for things, even when they're making a passive check. An elf leisurely strolling down the street will spot a penny on the ground, as if they were actually looking for that penny. But a human/dwarf/etc can do the same if they stopped and take the time to apply their whole senses, which when fully exercised may be stronger than the Elf's if they've invested in whatever skills being RPed. I personally imagine Keen Sense gives my drow, well, keener senses, but I fault no one else for claiming better ones without it.