Good climbers are equally comfortable in the saddle or out. But lots of riders don't know which technique really suits them better.
Find out by timing yourself on a favorite climb while monitoring your heart rate and perceived exertion.
Pick a hill that's typical of those you climb often. Ideally it will be between 2 and 5 minutes in length. It should be a good warm-up ride from home.
Each time you ride it, stay at the same heart rate and perceived exertion. The effort should feel "hard" but not all-out. Heart rate should be about 85% of your max. If you have a watts meter, climb at the same wattage each time.
No fancy electronic stuff? Then do your best to keep perceived exertion and your breathing rate identical on each trial. Remember your times and record them in your training diary.
Climb the hill standing the whole way.
Recover fully, then ride it again but stay seated.
Recover fully, then alternate standing and sitting.
Do this once a week for a month or so. Mix the order to help neutralize fatigue that may creep in by the third trial.
Along with your subjective perception of efficiency, you will have times that tell you which climbing method is more effective (faster) for you on hills of similar length and grade.
Bonus! Knowing how you climb best can give you a confidence that helps you climb better.
Source: RBR