Definatetly go with option #2, laying 6 courses of block in the trench on a 16" + wide footing. Here's the reasoning in my opinion.
- The trench will never be straight enough no matter what.
- The code in my area, footing width is wall width + 4" per side of wall MINIMUM. We always pour 20" wide footings minimum, as your footing forms will never be perfect.
- Even if you could trench perfectly straight, you would still need to line both walls of the trench with foam insulation, plywood, etc.. to have a smooth enough finish so the frost would not "pick" at the poured wall. Now by lining the trench, it's too narrow.
- Most inspectors in my area will only let us use the depth of the footing in the minimum frost depth equation if it formed. If we "bank" pour the footing, we need to add an additional course.
- I've often contemplated what your thinking of doing on small jobs, & have never found a way to do it effeciently, & more importantly, never thought it would perform as well as the conventional way.
Hope this helps your decision.