For me, it varies. I usually like to go for mid-range or moderately-priced locomotives that are either DCC-ready or already have a decoder installed, like modern Bachmann, Athearn Ready-To-Roll, Mantua Classics or Walthers Trainline. Heck, even an older Life-Like Proto 2000 locomotive would do nice. BUT, I have hardwired DCC decoders into a few Walthers Trainline locomotives from the 90s or 2000s, including a couple of Dash 8-40BWs and an F40PH, and with the Trainline locomotives it's fairly easy to hardwire a decoder into. (I'm actually looking to get a TCS T1 with harness soon to hardwire into my Walthers Trainline BNSF "Heritage II" Dash 8-40BW.) Maybe I'll then learn how to hardwire a decoder into those older Mehano locomotives (like the Mikado 2-8-2 steam engine and tender, or the Alco C628.) Even with DCC, I do enjoy running older rolling stock and sometimes older locomotives. With the former, I especially like running old A.H.M., Life-Like and TYCO freight cars that I upgrade with knuckle couplers and sometimes metal wheels.