First of all, let me just say that I am stunned that you had such a bad time with a Saito 100. I have had nothing but good experience with all the Saitos I have owned over the years, and currently have two Saito 100s mounted inverted in a P-38, running without on-board glow, with absolutely no issues. I get 10 -12 min. flights and land with plenty of reserve on 12oz tanks.

As for the Yak, none better IMO. I have flown just about every type of popular aerobatic airplane, and my Yak is the best so far. Very axial, and it just has no bad habits that I have found. You will love it, if you balance it correctly, as with anything else.

For gas engines, I prefer the rear induction (carburetor in the rear) due to the extra power (usually about 15% more) they are capable of producing at the same, or even slightly less, weight.

I have not owned either of the engines you are looking at, so I will defer to those with hands on experience with the supplied ignitions, etc.

For the size, the plane might be on the small size for a 26cc gasser. I would prefer a 120 size for that engine, which would get you in the 70s for wing span. They have continued to make smaller and smaller gas engines, but the ignition boxes seem to all be about the same size and weight. Wing loading is the key factor in a great flying aerobatic airplane. High wing loading can turn a great airplane into just an OK airplane.

I saw some new very small gas engines at the Toledo show. Much lighter than the ones you are looking at. They are due out in another month or so. Price will be less than a 4-stroke of equal power.