Drilling a hole and put a spacer in will be infinitely stronger than a
weld ,every time you weld something to the likes of a chassis
you create a soft point ie the heat of the weld will anneal the
metal adjacent to the weld and soften the metal around it
probably for what you are aiming for it will not matter that muchbut for any high stress joint in (and Im assuming you are
using m/s tubing )a welded joint will weaken the parent material
anywhere from 5-15% depending on the welders skills.I f you
are not confident in your welding ,hire a professional for the critical welds ...