I'll agree that Altoona is a significantly larger show, especially since it moved to the convention center. A beautiful facility. It's an easy trip for the East Coast N crowd which certainly helps attendance. Having prototype mountain railroading nearby, both modern and historical does not hurt.
I would not count Ohio NSW out however. The show will move to Marion, OH in 2025 and into a truly indoor environment at the fairgrounds. The Union County fairgrounds space in Marysville was maxed out and the quasi indoor environment had it's + and -. Same kind of prototype experience but different of course. No mountains to conquer but AC Tower and Marion Union Station are within a 5 min. drive of the fairgrounds. You will see plenty of trains and all kinds of equipment. T-Trak, N-Trak and FreeMoN are all represented. Less T-Trak than at Altoona. Fewer vendors but that might have to do with the past facilities, I don't know.