These two websites Gelbooru.com and Danbooru.donmai.us, hold a massive database of user-uploaded hentai images. You can find hundreds of safe and NSFW hentai anime images. Many people find that Gelbooru.com is much better than Danbooru.donmai.us due to its better search options.
When I checked out both, I did not find any difference. Both websites looked the same to me. I enjoyed the vast collection of both websites. Danbooru is disliked by people because you are not able to search more than two tags at once if you don’t have a full access account. Gelbooru has no restrictions on these kinds of searches.
Gelbooru has more tags that you can search for. This feature helps you make more elaborate searches according to your taste. If you want to search for images of girls with black glasses and ponytails at one time, you can do that.
Looking at the organic traffic of Gelbooru, it seems that it is much more popular than the Danbooru website. There is the option of buying their Gelbooru sticker if you want to support their website. The plus side of buying the sticker is that they would not serve any ads to you. You can block their ads by using an ad blocker, but that would be selfish on your part.
If you like these anime hentai image database websites, you should support them financially as it is very hard to run such a website without good contributions.