well.. American for me.. but i have always favored the ALCo S-2. The most popular unit of the S-series locomotives. Very versitile little units, even with several still operating on smaller american railroads.
For steam, i'll go with a ALCo 0-8-0, w/ tender. Like the S units, strong little brunts, but not very many survive today, if maybe 50-less. of course, all in museums.
Sean
I like the old Alco RS-3s and S-2s. There's something special about their shape compared to the modern units. The only modern units I like are the SW-1200s and SW-1500s
Steam: SP double saddle tank switcher. We have one here in La Mesa and it's a beaut.
American Diesel: Baldwin S-12. A handsome and solid work horse, still serving shortlines across the country.
Asian: Japanese DE-10. The JNR equivalent of the Baldwin.
UK BR class 06, 35 were built, 10 survived long enough to receive TOPS numbers. The last one was withdrawn from BR service in 1981, the one pictured still survives after a period in departmental use.
Don't be fooled by it's size, this is a very noisy brute! Try downloading the enginesound on the DLS to hear it.
Or for something a little more specialized, the Porter pneumatic mine engine that pulled the ore cars out of the tunnels and set them out to be pulled to the main line.
I hate to disagree with you but put those tri-axles on any type of yard that has any sharper curves in it, and you will start dropping cars, and engines between the grade, so it technically wouldn't be the best ever, except in certain situations. That is a beautiful picture by the way.
For my favorite switcher, it would have to be either an SW9, an S1, an S2, an RS2, a RS3 that has been customized with the low hood, or an MP15.