January is the month for penguin chicks, and it's the most searched single month for that reason. Gentoo incubation runs about 34 days from the Christmas hatch, so by mid January the colonies are full of the fat grey chicks people picture. Whales are building through the month, the sun stays up, and almost every landing site is open. It's the busiest and priciest part of the season.
If baby penguins are your priority, aim at the first three weeks. Hatching drifts by a couple of weeks year to year, so nobody can promise you a specific stage on a specific date, but that window gives you the best odds.
The 24 hour daylight is useful and disorienting in equal measure. Landings can run late, whale sightings at 10pm still have light on them, and your body clock has no idea what's happening. Bring an eye mask.
What you're paying for is certainty. January delivers the postcard version of Antarctica more reliably than any other month, and the price reflects the demand rather than any extra quality in the trip.