All of the protocols work equally well in normal conditions. However, Spectrum is by far the most popular brand going. At a large event, it gets swamped more easily than others, simply due to the popularity. Less popular protocols seem to preform better at this time. If another protocol would dominate an event, I suspect it would also suffer, perhaps even more than Spectrum.
I agree with LB.
The cost of the Rx is definitely a consideration. I only need 1 Tx but I use many Rx's.