El Garage Barber has been around in Medellin for 2 years now, their flagship location in Rio Sur. So if you need to plan to walk in, that would be your best bet to get a a clean, modern look that you would pay a fortune for in NYC or SF. The owner is from Argentina who was raised in Miami, honed his craft while living in the US, before opening his first location in Rio Sur.
If you are in Poblado, there is another location on Provenza in the basement of a building usually staffed with 1 barber. Best to make reservation.