**Straight Ability increases are your hands-down best way to increase AC as a monk.** 

Your *Martial Arts* class feature depends on being unarmored and *Unarmored Movement* only works if you are unarmored as well. 

You start out with no armor proficiencies so you would need to invest a feat to wear light armor anyway, whereas by increasing both Dex and Wis by 1 when you hit level 4 you will also gain the added benefits of adding +1 to initiative, Dex and Wis saves, skills that are based of Dex and Wis as well as increasing the DC of your Ki based spells/attacks by +1 and your to-hit and damage on melee attacks (assuming you are using a monk weapon) both by +1. 

Due to monks having a lot of class features tied to Dex and Wis its almost always in your best interest to increase those stats rather than to take a feat.