The SD70ACe and SD70M-2s have been my favorites recently. I like the looks of the SD70Ms with the flared radiators, kindve reminds me of the SD45s.
Im also a big Alco fan, especially the ones with notched noses and car bodies.
My all time favorite locomotive has to be the SD9043MACs with the SD70ACe cab in CP Red. While CP didnt care much for them, the pure size and rugged looking appearance of them appeals to me.