vBulletin 4 or 5 – which to choose

Few years ago I was running vBulletin 3.x forum and I am quite familiar with everything in it.
Now I want to start a brand new forum and I am thinking what to choose – I have vB3 license but it's seems kinda old nowadays.
Now you can get vB 5 with vB 4 but there is still little problem – I have no idea which one to use. I am running an WordPress site with news and information and want to make forum for it. I am also thinking about some integration between WP and vB like user registrations,…
vBulletin 4 or 5 – which to choose

See original post by Ksandr