Most detailed MTH scale size cars that are not box cars

My vote would be for either those drop-bottom gondolas or the 3-Bay coal hopper. Both cars came out only about 3 years ago and are highly detailed.

I'll second the drop-bottom gondolas. They're great!

MTH went through some re-tooling of Premier rolling stock. Some of the older tooling went into the Rail King line, while other items were upgraded. The more recent Premier offerings all have Kadee mounting holes and for a while included shims if you wanted to use Kadees with Hi-rail wheels. Modernly they don't seem to have those any more, but then they now also offer the scale-wheeled replacement trucks.

The more recent cabooses look pretty good, plus there were a couple of new caboose releases -- the UP with wood-beam trucks comes to mind.

The 64-foot 19th Century Passenger cars turned out way better than the catalog photos.

More recent heavyweight passenger cars have much better diaphragm detailing.

Another well done item is the Gunderson twin-stack cars.

The big "problem" with MTH hi-rail rolling stock is that they sit too high to allow for the hi-rail flanges. Installing MTH scale-wheeled trucks drops the ride height pretty nicely.

Don't forget the 100 Ton Grain car for Canadian Grain Train Affectionadoes!

I would suggest the drop-bottom gondola (mentioned above by several folks) and the 50 ft Airslide covered hopper.  I would vote the latter as the "most improved" Premier freight car from its earliest incarnation to what is produced today.

Like Matt says, height above rail is an issue.  I either replace the "as purchased" trucks with MTH scale wheel trucks, or use Atlas 50T Bettendorf, or 70T or 100T trucks.  The latter do "wonders" for the covered hoppers and coal porters.

I put Kadees on all my rolling stock, so the coupler pads/drilled holes are a welcome feature of the current rolling stock, though not all MTH Premier freight cars have gone this direction.

I would give the drop-bottom gondolas the "best in show" award. The tank cars are pretty nice, too. I wish they would make a steam-era tank car. 

I recommend the tank cars, twin-stack container sets and the covered grain hoppers.

Not including box cars, which MTH scale length cars are new or revised with scale details?

Since the mid 1990s MTH has created tooling for about 75 freight cars in the O scale Premier line. There were several new releases every year until about 2002.  Then their was a pause before a second wave of newly tooled freight cars with excellent detail began to appear in 2004.  Since the mid 2000s the older MTH Premier freight cars have received revised trucks and couplers and enhanced details.  Most, but not all, of the older cars have received upgraded underframes to accept 2 rail trucks and Kadee couplers.

Excluding the dozen plus MTH premier boxcars some of the very well done MTH O scale freight cars introduced over the last decade include:

The 36' wood reefer, 40' steel reefer and R50B express reefer all introduced in 2004.

The war emergency composite hopper from 2004.

The 41' flat car from 2005.

The fishbelly hopper introduced in 2007.

The 70 ton 3 bay hopper from 2007.

The steel and composite GS gondolas introduced in 2009.

The four wheel bobber and the UP CA-1 cabooses are excellent models.

All of the cars listed above are from the steam or steam to diesel transition era.  For more modern diesel era cars MTH has also introduced the following.

The funnel flow tank car from 2004

The coke hopper from 2005

The 60' flat car from 2007

The earlier diesel era MTH Premier cars to receive significant detail upgrades include:

All of the covered hoppers.  This includes the 70 ton PS-2 and the 100 ton 2 and 3 bay ACFs, PS-2CD, Airslide and Canadian Cylindrical hoppers.  The 4 bay Canadian hoppers are particularly nice.

The center beam flat car.

The 20,000 gallon 4 compartment tank car.

The CN/Auto Train auto racks.

The 100 ton 4 bay coal hopper.

The Coalproter gondola

Steam and transition era freight cars that have received detail and underframe revisions include:

The 50' flat car.

The 50' gondola.

The 2 bay offset side hopper.

For more you might want to check out the O Scale Freight Car Guide. 

https://ogrforum.ogaugerr.com/t...le-freight-car-guide

Great reference, been catching up!

My favorite is the N6-B caboose. The sprung trucks are unique.

I recently got a MTH caboose (thanks again Martin), it was listed as a N6b, but upon further searching it turns out to be a NDa:

Like the one prohobby shows, it's very well detailed, sturdy, heavy, and has pads for Kadee couplers, interior w/figure, lights, and marker lanterns.

This is the one I've stripped the paint off and am going to paint it for the Norfolk & Portsmouth Belt Line being PRR sold them to the NPBL.