I've had a W205 for two and a half years now, and the AC performance is average, at best. Compared to, let's say, a Corolla and Civic it's much worse.
Mine is AMG line with all black leather interior and panoramic roof. The panoramic roof cover is really thin and it doesn't filter out the sun much, which really heats up the interior. The center console with piano black finish also gives off a lot of heat. So even on long drives during daytime it struggles to offset the incoming heat. Point is, if you go for one without panoramic roof, I'm sure the AC performance will be a lot better. The AC is fine during night time.