Hurricane Electric AS6939

The price is usually amongst the lowest you'll find. I've found them
very easy to work with. They have a pretty capable tools development
team in house. They don't do communities other than RTBH. They are
doing ROV, which I think helped clean up some BGP noise I used to see,
but I've not checked lately. They also know a thing or two about IPv6,
plus carry traffic for all those IPv6 tunnel broker setups and probably
at least if not more of the 6to4 traffic for whatever is left of that
if it matters to you (and I might argue you might want to consider not
accepting the 6to4 associated prefixes nor carry that traffic). Make
sure you maintain another way to get to Cogent-only prefixes.