My service provider offers both at no extra cost so it's a Q of what's best. I have had static for a year but not done any BH stuff as such but download a few things they probably wouldn't like although not a lot.
Reading further about this - with dynamic IPs, the ISP knows exactly which IPs have been assigned to which user at which time so no real anonymity there. Also, given the fact that the range of IPs is likely to be limited, if someone wants to find out who you are, I don't think it would be difficult.
So my take is that there's not much in it and may as well stick with static and use proxies if anonymity is required.