Quickest is either WCS94 or T3 as i only had them for about 3 months each - great to play onsite but in a small collection i found both were too easy and not deep enough. I like my machines to have modes and rules.
Longest is Shadow and i find it is a great challenge and i have had it for about 2 and a half years. It was my first machine and i cannot see me moving it on anytime soon if ever.