Both. As mentioned, Lionel's is based on the streamlined rebuild in 1953, of which E-2 survives in St. Louis. Mine is the first TMCC one, in UP colors. I picked it up thinking I could shoot it all black for that 1919 look, but the body style is all wrong. Now looking to swap it for a Non-UP style, either brand. Decent engine, definitely appreciate the control switches being below a removeable hood panel. No smoke unit. All the Lionel TMCC features you'd expect.
I also have a MTH bipolar, PS2 version in 1940s? colors. Silver stripes on noses. The original body style, though none perfectly replicate the as-delivered 1919 look, without the famous crooked-box logo. These were not used in the Mountain division until after their 1953 rebuilds, but the PSA clearly states "Welcome to Harlowton [MT]." MTH's has a smoke unit to simulate the oil fired boiler for steam heat. I can tell you from experience this is not an easy locomotive to work on internally. It's diecast and a decent puller, though I get some slippage and struggles in conventional running on slight inclines if I'm pulling my full 10-car GGD Olympian Hiawatha set.
Overall two styles of the same historic locomotive, neither will satisfy the rivet counters but either will look good running a layout, preferably through some some mountain forest scenery.