If you mean "out" gay population, it may possibly be the Unitarian Universalists. If you just mean sexual orientation, then it's likely that all religions have about the same percentage of gay people within their ranks.
Christianity
The country with the highest gay, lesbian, bisexual, and transgender people is China. While not all countries publish their census data and sexuality is not often a census question, human sexuality is as diverse in every country as it is within the USA. This means that because China is the most populous country in the world, they have the highest homosexual population. California has the highest population in the USA and thus has the highest population of homosexuals.
christianity
Judaism (75%).
Islam
The state with the highest population of homosexuals per capita is District of Columbia with an 8.1% gay population.
Most probably San Francisco and Miami.
Christianity has the highest population in the world, with over 2.3 billion followers.
Scientists believe that the worlds population is 4-10% gay or lesbian, and another 25% to be bisexual. A 2009 United States Census Bureau statistic shows the highest population as California at 36,961,664 so 4% = 1,478,466 people minimum.
China has the largest population in the world, and therefore has the largest gay population in the world. However, the majority of LGBT people in China are closeted.
Afghanistan is the country with the highest percentage of Muslim population.
Its muslim! Sorry but no Christianity is still the largest religion in the world. Approximately 31.50% of world population.