I've been happy with mine - I have a solid enough telescoping one like this one (http://www.amazon.co.uk/York-Fitness-60033-Doorway-Chinning/dp/B000N3T1CC) where you screw two pieces (holders for the bar?) into the sides of the door frame.
Has held my 75/ 80kg frame for many years with no issue. Door frame is sturdy enough and mounted into a solid internal wall (ie not plaster board/ dry wall).
Hope this helps, and in fact I have two as they were cheap enough, with the second one mounted at hip height for bodyweight rows. I leave the pullup one in place, but remove the one for rows when I'm not using it.