Like it was said before, it all depends on your energy state and what your trying to do with the bandit. Even in a spiral climb though, there are times when I kick flaps out to tighten the spiral to either make the bogey think he has a shot, to turn inside him, or to accelerate a stall to fall down onto him. Flaps and a little throttle control,down to 25% then back up to 100% done in about 3 seconds really helps get over the top quicker, tightens your circle, but you are giving up a little bit of energy.
The people that are making the quick merges or reverses on you are doing one of three things. One, they have setup for a lead turn, which can take place on any merge, doesn't have to be the first pass to qualify for a lead turn. Two, have a big difference in energy, them being much slower. Three, CO-E, have a better turning plane. Alot of what you see a good stick doing is just an illusion of camouflaged energy state.
The best thing to learn is how to judge the other person's E state. How fast he is going, and his alt position compared to yours and then relate it back to how your planes match up, then use it against him.