Atlas Trainmans have a better, quieter drive, are easier to convert to DCC (since it already has a light board in it with a 8-pin plug), and the shell is easier (for me) to get on and off. On the other hand, the detail of the Trainman is akin to the older Athearn Blue Box GPs (no grabirons, etc.).
The Athearn GP38s (and the basic $50-$70 line, including GP40s and GP50s), have some good detail, and run well. To convert to DCC, I recommend getting out the soldering iron, a TCS T1 decoder with harness, some of that high-temp tape, and either get a resistor with a couple of LEDs, or totally disconnect and not run the cab light the locomotive comes with. It's a little bit of work. I thought the hardest thing was to isolate the motor from the frame, but doing the LEDs is more difficult. The Digitrax DT or DH123AT (with the harness for the non-quick plug Athearns) has too much wire, and you'll have to cut some of it off or tie it off to prevent it from getting wrapped up in the flywheels and drive shaft.
They went quickly, but my favorite GP38-2s were made by Proto2000. Some places still have them. They have a great level of detail, good weight, a good quiet drive system, and are DCC ready. The only issue with them is to disconnect and remove the number board lights (front and rear) since the factory wired them to the motor or track pickups (can't remember off the top of my head) and if left in place, the electricity will damage the decoder.