I've found modern Netgear and ASUS AC models to be very reliable. While there is almost no benefit to an AX model over an AC model, it's his money. The Netgear R7000 or ASUS RT-AC68 would do very well at a reasonable price.
HERE is a good site for comparing routers using rigorous testing.
The reason I ask, is there is a big difference if this is pre-show and there are not hundreds of cell phones generating hotspots or other interference like that or during the show. Biggest thing, would be to get some elevation for the router. Sitting 8-10 ft above the floor level would be best.
You can't believe coverage numbers they are pulling those out of their ass. It all depends on how you define "coverage". This is sorta like "unlimited" cell phone plans.
Using the very technical definitions used by the FCC to certify equipment almost all routers will transmit the data the same distance. The power level of the signal is regulated by the government and almost all router transmit at maximum legal power. Now its hard to say how these companies get their numbers. Some actually assume you are using multiple radio sources and repeaters. Others include things like transfer speed but don't actually state the rate they are testing. This of course ignores the fact the the most common problem is the end device. Something like a cell phone has small antenna and low power transmitter to save battery. So the phone might be able to hear the router but does not have enough power to return the signal.
The way you get more coverage in large areas in addition to using multiple radio sources is you use directional antenna so the allowed power output can be concentrated where needed.
I suspect this is going to be test and see what works type of question.