You have to decide exactly what you really want, if it is to spend the minimum amount of money possible than go for that.
True and whilst price isn't a major factor in the choice, I do sometimes wonder why I pay the extra £10 a month to Zen for, compared to say the Sky deal mentioned. I guess the potentially better customer service. Wouldn't of thought any of the mass market ISP's would suffer congestion issues now. Well, maybe Virgin still do but that would be localised.
Static IP - nice to have but I only really find it useful for the Thinkbroadband BQM. Can use a DDNS to get around any changes to the IP address.
IPv6 - again a nice to have but not essential.
Content filtering - I'm guessing this is if an ISP potentially blocks a website? I don't think I've ever had that issue.
Latency - purely going from a BQM, Sky had the lowest latency, 9-10ms, when I was previously with them. Zen were initially around 10-11ms but it increased to around 14ms. Presumably a routing change. Nothing major but I do occasionally play some first person shooters.