I know I'm getting in to this discussion quite late, but thought I'd throw in my opinion too...
I always used Insight, until The IT Index introduced themselves to me, their prices were always fantastic, so couldn't justify using Insight - I was let down by late deliveries far too many times, but carried on using them until Insight could offer us the Catalist pricing...
I do still use The IT Index, but if we're desperate for something, it'll usually go straight to Insight...
I must admit, then in cases where delivery was late - Richard (posting above) always got it sorted fairly quickly