D is probably the easiest but you have to get used to not playing the first 2 strings. If you learn an E chord first you can move it up and down the fretboard and get some additional chords out of it. Like start 12 frets up and move down a couple of frets at a time makes a nice sounding song.
Once you get the E chord down, it's a simple step to move on to barre chords.
Just learn to press your first finger across all the frets while your other 3 fingers do a chord in the E shape.