For me the rule of thumb is an ISP with:
1) A static public IP
2) They meddle with my traffic as a little as possible.
Once Zen gets large enough to be subject to the court orders blocking sites, I will seriously reconsider my position. Its not even that I visit those sites (and if I did there are VPNs), its the principle of the thing and the potential for the blocks to be implemented badly as Plusnet have done in the past as I recall.
Plusnet were my first ISP and I only left when they started badly implementing traffic limiters that caused my Usenet usage at the time to be throttled 24/7, when it was only supposed to throttle after a certain amount of traffic per month.
Its kinda ironic however that moving back to them for my second line caused the drop wire damage to be discovered and ultimately fix my Zen line, which I wasn't aware was faulty.