The answer to your question depends on a few factors. I will assume you are shooting standard ATA registered targets and not international. The biggest factor is whether you are a quick shot who picks up the target and pops it immediately or do you ride the target a bit? A quick shot at 16 can get away with a more open choke and gain a bit of an advantage.
At 16 yards you want the most open pattern you can get that does have holes lager than the target at the range of impact. I like #8 shot at 16 yds because it puts a little more lead out. However, I am VERY quick on the trigger at 16 and most hits are "smoke" even with an open choke. If you are slower on the trigger the smaller shot may cost you targets at longer range unless you tighten the choke.
From 16 yrds I generally will shoot a modified or improved cylinder in competition depending on weather and wind conditions. I generally tighten the choke and move to a 71/2 shot for handicap when money is on the line. I always practice with the tightest chokes I have with 1oz loads. For competition I use heavy loads with as much shot as possible. Of course if you are just shooting for fun use what you have. When the money is on the line take all advantages.
It is best that you experiment with the shot and chokes to adjust to your "quickness" and the range you generally engage your targets. Once you figure out your general range of impact you can use a pattern board to play with shot density patterns using various chokes and shot size. If all your targets are "smoke" I would open the choke and see what happens.