bear's lair:
I am modeling a late 1930s west coast logging rr in ho scale steam powered, with lot's of inclines with mountains and hills and a large forested area with two trestle bridges on about 95ft of track,
You didn't really define a prototype, or what a good model locomotive means to you - other than durability and weight. How important is prototype fidelity? Slow speed performance? Does it need to be quiet enough to install sound? What level of detail? Price range?
Probably the most important - how much work are you willing to put into this model locomotive to achieve the other goals? Is a kit acceptable? How about a true bash? Or building a Class A Climax from a bare mechanism? Are you willing to chase down out of production items, or outbid others on eBay for a particular model?
Some of the characteristics of logging railroads - California, Oregon, and Washington coastal. The 1920s were boom years; in the 1930s the nation was in the Great Depression. Not much new was bought in the 1930s, and many outfits went bust. Those that survived generally converted to truck (with a few exceptions) in the 1950s. The logs were generally pulled downhill to the mills; empty cars went back up the mountains to the landings. Because of gravity, tremendous power was not needed by the logging railroads. Mining railroads usually needed heavier engines than logging lines. A geared engine is/was pretty much limited to less than 30 miles each way out and back in a day's work. Rod engines were used if a longer run was being made.
At the most expensive end are brass models of geared locos. These will meet your weight and durability criteria better than anything else. They may need painting and/or remotoring. I believe the PFM B-2 Shays were made somewhat oversized, but the others are more to scale. Shays were built in a wide variety of sizes, but the very largest would be used in mining and not in West Coast logging. Model Shays tend to struggle more than Climaxes or Heislers on very sharp curves due to the offset telescoping line shafts. They will usually go better around sharp curves in one direction than in the other.
Brass logging rod engines - 2-8-2T were the most commonly made models - would also be a good choice. NWSL in particular imported these. There are no good non-brass examples that I know of, although a Proto 0-8-0 might be a good starting point to rolling your own.
Mantua's 2-6-6-2 (either tank or tender) is a good generic representative of the Mallets that were found on some West Coast logging lines. There have been reports of poor electrical pickup, but it will apparently take 15" radius curves with ease.
Bachmann's Shay is a very nice model of a quite large 3 truck Shay. It does have the issue of cracked/stripped gears, but NWSL has come out with steel replacement gears. The Bachmann Climax (out of production) apparently has the same issue, and again NWSL is working on a fix. Heavier loads tend to exacerbate the problem with the gears.
I have not heard anything negative about the Rivarossi/AHM Heisler other than it too is oversize for a logging line - it scales out to some of the largest Heislers made. Supposedly the '90s version has slower speed gearing and other improvements. Mine is the earlier version.
If you are willing to tinker with the mechanism, the Roundhouse Shay makes an attractively sized Shay. NWSL regear kits are available to improve the mech, and there is plenty published on how to make it run well (with some effort). I have been told that the Roundhouse Shay repeated the slightly oversize scaling of the PFM B-2, but is still reasonably representative of a 50T Shay in the 2 truck version.
At the more adventurous end is the Keystone Shay kit. It requires an NWSL motorizing kit to run, and is not, according to the NWSL instructions, "for the faint of heart." However, it is all metal, and builds into a very nice pulling, very small Shay. There is help on the web.
Also at the bash end of the spectrum would be taking an 0-4-0 or 0-6-0 mech and making a 2-4-2T or 2-4-4T or 2-6-2T. All were common logging rod engines. The Kidder, Mantua, Spectrum, Roundhouse mechs could all be reasonable starting points. Roundhouse even made a 2-6-2 kit which might easiest to convert.
At the cheap end was/is the Roundhouse Class A Climax. Roundhouse made a rather fanciful steam shell to fit their boxcab diesel chassis. Noiser than all get out, mine outpulls and switches at slow speed better than any other locomotive I own. Ultra-reliable and very heavy it is; quiet it is not. NWSL refused to make a regear/remotor kit because the kit would cost more than the locomotive is worth. Again, literature exists on how to make it run better and look better.
Plenty of modeling logging lines use the Heisler or Bachmann locos despite their size, and their owners are quite happy. Only a few "rivit counters" know or care about the difference.
my thoughts, your choices
Fred W
....modeling foggy coastal Oregon, where it's always 1900....