I think that it would be great to have the 2 machines!
Oberheim synths - my preference is going to the OBXA or 8 Voices - are one of my favorite poly synths - incomparable for their thick polyphonic sounds.
ARP - 2600 - is one of the best mono synths, very different than the Mg ones.
Its semi modular structure is very oppened and nice to explore new directions of sounds.
