I would vote for the Monon set as the clear winner from the Big Two this year (Lionel & MTH), it is a great looking train and shows what either of the Big Two can do with the support and hand holding needed to get the details right. Excellent work on Steve's part.
Overall in O scale, the passenger train of the year as to go the GM Train of Tomorrow, between the specially engine and each car being entirely unique, it shows what can be done overall -- although for production reasons I cannot image either Lionel or MTH even attempting such a thing. Scott has done wonders with small runs over the years, this year the Canadian and ToT are prime examples, I am sure next year the El Capitan and perhaps Cincinnatian will be in the running as GGD / 3rd Rail continues to produce top of the line passenger sets in a scale size.
I like the idea of the best new to me category as well, this year that would have to be the GM Train of Tomorrow, closely followed by the K-Line Greatn Northern Empire Builder, and the GGD Baltimore and Ohio Columbian, with high honors going to the K-Line California Zephyr as well.
On the whole it is a golden age for those of us who love passenger trains, between great new specially releases like the Monon set from Mr. Muffins & MTH, to Scott Mann and GGD / 3rd Rail coming to market with new full scale trains never before done in O or not having been done in many years or with the high level of detail standard on all GGD products.