Jet ventilator. You can't get enough pressure/flow with an ambubag or the machine circuit. Exhalation is passive, once you get the lungs inflated, even if you can't intubate/ventilate from above, a full pair of lungs will still exhale passively through the upper airway. But the extremely low pressure/flow you get with the ambubag/circuit through an angiocath won't get much into the lungs since the low resistance path is up and out. You need to use the jet ventilator. IMO the whole angiocath + 3cc syringe + ETT connector is mystic MacGyverish lore dogma and should die. If you ever get a chance to do a cadaver lab try it both ways. Low pressure/flow through an angiocath Doesn't Work.
I suppose if you sealed the mouth/nose while ambubaging an angiocath you might get a tiny amount of O2 into the lungs and that's better than nothing, but you're far better off just using the jet ventilator on the machine.