Your question can be answered in two ways. We can consider numbers of species. Or, we can consider numbers of individual organisms.
In terms of numbers of species, insects certainly represent the largest percentage of the world's organisms. There are more than 1 million species of insects that have been documented and studied by scientists. And the total number of documented species of living organisms at the present time is probably about 2.5 million. So insects represent about 40% of all known living species!
But that's not the end of the story. Scientists estimate that there may actually be somewhere between 10 and 30 million species of insects inhabiting our planet. So insects as a percentage of organisms might actually be greater than we currently estimate.
If we look at your question from the point of view of numbers of individuals, the answers is almost certainly insects as well. In fact, the answer may be ants. There are 14,000 known species of ants. And they all form ant colonies. In some species of ants, those colonies may be extremely large. One colony may contain many tens of thousands of individuals! Some scientists have made credible calculations suggesting that the weight of all ants is greater than that of all humans.