Miter saw all the way. Perfectly clean square cuts at the precise spot you want them. Quick and easy. I'd rather take the 2 minutes to roll the saw out and set it up versus do a single cut by hand. It's a bit overkill to use a 12" dual bevel compound sliding miter saw to cut a stick of pvc but it's also very satisfying.
Speaking of rolling it out, I like to just put it in the driveway. Easier cleanup and if some sawdust escapes, it's not a big deal, versus having it set up in the garage where the airborne dust settles on the bikes, tools, etc.