JFYI, if you want different C class for SEO reasons, that's a myth, you wont get any difference on the Search Engines positions having sites hosted on different IPs. If you have a link farm, you'll penalized no matter if you are on the same or different C class.
It'd probably be best if you could give us some more specific as to what you need. Perhaps specs on the server? Number of visitors, or monthly bandwidth, etc?...
Managed, unamanged, vps?
I want the host to use for SEO
managed, Host 5 sites with 50k per day(all),3 dedicated IPs,
JSON, DOM, SimpleXML, MySQL, PCRE
PHP GD extension
PHP cURL extension
ImageMagick installed on server
Access to cron on server
I believe EuroVPS still allows adult content, on reserved IP ranges. Contact sales, ask them.
Does Hostgator allow adult?
Hostpolar allows adult content if it's not the main focus of the site. (No porn sites.)
It will depend on your budget to decide if you need to get a VPS or go right into a dedicated server. Also any idea on your monthly BW needs? A simple way to find out is a hosting provider allows adult content is to ask them. There are alot of hosts that do allow "Legal adult content" they just don't promote it.