It’s hard to argue against the SD40-2! (Just remember that Conrail’s had Flexicoil trucks, not the standard HTCs)
Conrail also had a huge fleet of GP40-2s (120+ of them). An iconic image is four of them on van trains (intermodal). Later they were mixed with B36-7s (60 of them) and B40-8s (30 of them).
If the 1990s is your cup of tea, the iconic locomotives of that era would be the SD60M, SD60I, and C40-8W. They were the mainstays of the road fleet.
The “best” of Conrail would be the SD80MAC. It was the most “Conrail-ish” and blended all the up to date technology. It was state of the art when built. AC traction, radial trucks, electronic fuel injection, electronic air brake, Ultracab II cab signal/speed control, integrated flat panel displays, isolated cab - and it all worked! (they are still in service 20 years later)