While I have my favs, I think that whatever trains I'm running at the time (especially if they are running well) are my favorites at that time.
Amongst 12* other sets on the layout at this time, my 2343 Santa Fe F3 A-B-A pulling 6 PW aluminum passenger cars is on my upper lever. Gotta be one of the most beautiful sets, especially with the extra cars. O42, O54 and O72 curves on that level.
*Most on sidings - I can run 6 sets at one time but I usually get in trouble doing so (I have a 45 degree cross track allowing two separate loops to cross so one has to pay attention or a broadside accident will happen). 4 sets running at one time is fun, however, plenty of Post War "railsounds" from the tracks, motors and e-units.
Sorry Arnold, I know that I went well beyond your question here. I get carried away.