The numbers are for the link to a doujin. Most of the time, its nhentai(dot)net/g/<numbers>. But they could also be numbers for a different doujin site like pururin or tsumino
I don't really have a particular favorite doujin. I usually just browse through the yuri tag lol.
doujins(dot)com has voiced doujins which are fairly new and add a little to the experience