A black leather interior is like entering a hot cave, but you get used to it pretty quickly. Black interiors are easier to maintain since you don't really have to worry about stains, and if the leather is cracked, black hides it better. Black is also very, very common in most cars.
Lighter interiors feel more "open", and will be slightly cooler in the sun. They are harder to maintain due to the risk of staining and cracking over time. Lighter interiors also appear more upscale because they aren't as common as black leather.
Whatever you have, clean, condition, and protect the leather to keep it in the best shape possible.