S2. Or the gf series

The GF series has changed multiple times over the past years. I prefer the older wide blades for iron piston .15's. The new GF series work well on the LA/FP.15's. I use 7x4's. I do find them to work well on the Fox BB .15 in the 7x4 range. I find 7x6 props load the engine too much. If I find the need to use 7x6's on my .15's I take them and round off the tips shortening the diameter and making the prop more efficient. I scrape the prop to thin it as well and this has worked fiarly well on my Clown racers.
On smaller engines such as Cox, I cut the 6x3's down to 5". They make a 6 x 3.5 which I use on the Norvel .074. Most places carry the MA props. I find them to be typically out of balance but they're cost makes up the difference. We fly at a field at certain times of the year that usually breaks the props on landings. I find them to be problematic at times on Mccoy redheads because the prop driver doesn't initially seat on the back of the prop due to the bumps on the driver. It usually takes repeated tightening until it seats.