That all depends on the plane in question. I had a Midwest AT-6 and it was definitly not a good practice to do 3 pointers. Landing on the mains was best as most large warbirds are. I have a WM Clipped wing cub that I do 3 pointers with every time. If the plane does not have bad stall characteristics then 3 pointers are fun and sometimes challenging to do. If she has a bad tip stall or any other bad stall tendency then main gear landings are probably the best.