The Metro: fast, cheap and busiest at rush hour
The Sistema de Transporte Colectivo Metro is the backbone of the city: twelve lines, 195 stations and a flat ticket bought at the window or from machines, with rechargeable cards sold at most entrances. It runs roughly from 5am to midnight on weekdays, later on weekends. Line 3 between Indios Verdes and Universidad is the workhorse for Roma, Condesa and Coyoacán; Line 7 serves Chapultepec and Polanco; Line 2 links Bellas Artes, Zócalo and the eastern bus terminals. Trains are frequent, but avoid 7–9am and 5–7pm if you can, when carriages are genuinely packed.
Pickpocketing is the one thing to plan around. Wear your bag in front, keep phones out of hip pockets and skip the first and last carriages, where crowding is worst. Transfers inside stations involve a lot of stairs and long corridors — Pino Suárez between Lines 1 and 2 is a hike — so pack light and don't schedule tight connections. For most visitors staying in Roma Norte or Juárez, the Metro is the fastest way to reach the Centro Histórico, Coyoacán and the Basilica de Guadalupe, and it is hard to beat on value.
Metrobús: the surface option that skips traffic
The Metrobús is a bus rapid transit network with dedicated lanes and seven lines. For travellers it matters most on Avenida Insurgentes (Line 1), which runs from Indios Verdes in the north down through Reforma, Roma and Del Valle to El Caminero in the south; Line 4 loops through the Centro Histórico and connects to the airport terminals. You need a rechargeable card from a station machine — the ticket is not sold in cash on board — and you tap in at platform gates. Stations are elevated in the middle of the avenue, so you cross by footbridge.
Line 1 is the practical choice for moving between Condesa, Roma and the Centro without changing trains, and Line 4 is genuinely useful if you land at Benito Juárez and your hotel is downtown. Buses are slower than the Metro in the evening peak because signal priority is imperfect, and the crush at Insurgentes station around 6pm is real. I would use the Metrobús for short hops along Insurgentes and take the Metro for anything crossing the city. Both require the same card, which makes switching simple.
Where to stay to make the transport work
Your neighbourhood choice does more for your trip than any single transport decision. Roma Norte and Condesa put you within walking distance of parks, cafés and Line 1 Metrobús stops on Insurgentes, with the Metro at Insurgentes, Chilpancingo and Sevilla. Juárez and Zona Rosa sit between Reforma and the Centro, handy for Line 3 and the Metrobús. Polanco is quieter and better served by taxis than by rail; Coyoacán is lovely but needs a bus or taxi to reach the Metro at Viveros or Miguel Ángel de Quevedo.
Book earlier rather than later for stays in Roma and Condesa, where small hotels fill up around major holidays and the December–April dry season. For a first visit I would choose a hotel within a ten-minute walk of an Insurgentes Metrobús station: it gives you one card, two modes and a straightforward route to the Centro, Coyoacán and the airport. Check the exact walking distance to the nearest station before you confirm, and you will spend less time in traffic than most visitors.