The question is anachronistic. GM spun off Electro-Motive in 2005. It's now a subsidiary of Caterpillar.
To reframe the question: Alco/GE vs. Electro-Motive? Alco built diesels with GE electrical components, and in the transition era was EMD's most important rival. Then GE started making their own locomotives and Alco went out of business - not sure of the exact dates and sequence, but certainly GE took over from Alco as EMD's biggest rival. Now GE outsells EMD, but we will see what Caterpillar can do.
Personally, I'm a Fairbanks-Morse guy. F-M was right on the Milwaukee Road, and the Milwaukee ran a lot of F-M locomotives. Besides, a locomotive powered by a WWII submarine engine is just too cool.