What is your trooper Locomotive(s)?

My "trooper" engine is my Lionel PRR Mikado Jr.  Got it in 2007 and it's still running great and is probably still my best sounding engine.

The Marx CV that I dug out of the  dirt floor garage comes to mind.

Without a doubt, my 736 Berkshire from my first train set. Upgraded to electronic reverse unit but otherwise original and still runs great. I have a MTH RailKing N&W 611 and Milwaukee Road Hiawatha F-6 4-6-4, and more recently the Lionel Legacy Milwaukee Road S-3 4-8-4. They are beautiful locos but that Berk has always been my sentimental favorite.

Atlas SW9's

Definitely my MTH railking New York Central Dreyfuss Hudson and matching semi-scale railking cars.  Even as we clear out the modern MTH to switch to older postwar stuff, i plan to keep it on the roster. great engine and entire consist!

My Lionel 1951 2026.  Been running, whistling and smoking just fine since Santa brought it to me in 1951.

Most definitely my MTH Railking Scale Amtrak PS 3.0 FP45.  This thing is a powerful puller. I was having trouble with (2) K-Line TMCC F40PH's to run in sync when I decided to go out to my car and press her into service with (11) Weaver 20" Aluminum cars and the matching non-powered unit in tow.

just about all of them. My Pre & Postwar 224E,225E,671,675,1666,736,2046,2055,Marx 333,666,999. Just occasional lube.my MTH RK M1a has only left the tracks for a new teather and traction tires since I got in 10 years ago.

I have a 2056 Hudson which is always put up whenever the rest are having some maintenance so I guess she would be the go to loco. Still ticks over like it was 1952.

I have two.

MTH proto-1 Santa Fe freight f3 set. I bought it used about 10 years ago, installed a bcr, and it just keeps going, and going, and going...

Williams ten-wheeler. Sadly, the most accurate engine being made at the moment for my time-period and prototype. Never a problem with it, even the smoke unit still works well after 2 years of pretty heavy service.

This one.

Several Weaver locos from early 1990's, all PS2 and all solid as the Rock of Gibraltar and utterly reliable.