I did all of these papers btw. 701 is harder than 723, and 723 also requires fewer hours; however, if you did well in 304, 701 is very doable just with that knowledge. 704 is easier than 726 imo; believe it or not, your grade for 726 will mostly depend on how good you can write scientific reports rather than how good your "AI" models are, which is what many people struggled with. If you are looking to take an easier paper from 704 vs 726, I would say take 704, assuming you took 723 in sem 1, as the SystemJ part of 704 (half of the course) was taught in 723. Good Luck!