As Crusty said the 23012 would be a better choice in my opinion of the 3 you inquired about. The drawback is that it must fly at a higher AOA. The M6 was a modified Clark Y to kill some of its lift at higher speeds (early Pitts). The 23012 was a modified (I forget which) section …….. it was modified by just lowering the LE radius in a NACA wind tunnel experiment...……. worked out great. Was used by a lot of aircraft …..like the Helio Courier/Stallion, Taylorcraft, a lot of Beechcraft up to 23018 or 18% thickness. Don't overlook a good section like the NACA 1412 (Decathlon) if you want to do any aerobatics.