Free adult blog services without banners are guarenteed to introduce banners when they get bigger. Why? Because this business is not charity, they must pay their hosting bills and support desk.
A exception is google and some other major company like adult.com they have enough resources to offer a bannerless service. But sooner or later banners will appear.
Now you have 2 choices:
1. go with a bannerless service and be cheated hard after a half year.
2. go with a service like thumblogger. With thumblogger you know what you get: a small topbar.

Above all thumblogger is in the business for over 1 year, the other services are just 1 or 2 months old. I've seen already 3 adult blog services in a half year that were shutdown and their blogs were deleted.
Now i ask: would you want to build a blog with traffic and all and discover on 1 saturday morning that your blog is gone? I don't think so.

History tells truth: bannerless hosting, like we all know it did fail, no one can deny this fact.