As a friend of both Rich & Ivan I have to say BOTH are equal but very different shows.
Ivan does a hell of a good job with the Allentown Show but that show has grown to a point of just craziness. It is super busy from opening right up to closing each day and a high energy show. The flea market area is likely the best in the country and is my favorite part of the show. The down side with Allentown is it has grown to a point of almost not being fun anymore. Really busy, really noisy, and just plain crazy pretty much all day. Farmers market food right across the street is another great thing about Allentown! (If you like busy & high energy Allentown is just that).
On the flip side Rich has a totally different approach to his York Show - he isn't looking for HUGE - craziness - etc. It just has a nice feel to it - very relaxed and still a lot of fun. Rich runs the show more like he is dealing with family & friends. The show just has a great feel to it - like your old favorite pair of shoes! I actually set up for the first time as a vendor at York this past year and it exceeded all expectations actually doing better than Allentown for me. York typically has shorter lines for freeplay machines and a lot more earlier stuff including "Bingo Row' and a nice selection of woodrails & EM's. There are still plenty of newer machines but nothing like the selection at Allentown if you are into newer stuff.
Asking which is better is like asking a parent which child is their favorite. If you can make both shows - go to both. If you can only get to one or the other flip a coin and do the other show the following year. You will not regret going to either!
Size wise I would say Allentown is 30 to 40% bigger than York with a lot more vendors selling new parts & mods. As far as freeplay machine count I think Allentown is typically around 275 and York just over 200. If Ivan or Rich reads this post they can verify that count. I know this past year Ivan had to turn machines away due to freeplay area being 100% full on Friday. I am not sure how Rich did but I think he was at least close to full Friday (maybe room for 20 or 25 more machines at a guess).