My vote for worst echos others , GE U25B , but I have to qualify that only up to the transition point were they slow, then not too bad. 16 notch tiller for a throttle not easy to use, especially running long hood. Current worst has to be GE P32DM (MetroNorth)but without any qualification. Must be in the software as they just take FOREVER to get going. At least they're comfortable inside with A/C and reclining seats. All time best to be able to work and feel the train is the EMD GP-9. Not overly comfortable but great to run. SD40-2 a close second.
In my opinion the worst to operate are anything by GE . I love SD70's and SD75's . CN 5600-CN5800 GP 40's are ok and so are GP38's .
