My personal recommendations for places to eat ramen in Mexico City... and some sushi as well
Beautiful small place at the corner of Medellín with Álvaro Obregón, very low prices and tasty, has a vegan friendly menu and portions are small compared to other shops but allows for trying many different things.
One of the purest ramen and sushi places in the city, at the heart of Zona Rosa, it's divided into the small ramen shop and the full restaurant (Wan Wan), the ramen is served in both sides but the small ramen bar only seats 8 people and only serves ramen. Quite a busy place, sometimes you'll wait about half an hour for either place.
This is the restaurant of one of the owners of El Mog, after they split this one became a very good destination for Japanese and asian cuisine. Varied selection of dishes. A bit pricey for what it is. Really crowded on weekends.
My main recommendation, you'd be better of calling for a reservation because it's busy but booking an hour ahead should be enough. Amazing dishes and the ramen is tasty, very good noodles. Get the Callo Mayo sushi too if you're sharing with someone.
Small chain of asian food restaurants, somewhat commercial but still very good, nice atmosphere, great variety of sushi and cocktails.