I'm curious why you're looking at the RX-V1800 rather than the 3800. The latter is in the same price bracket as the Pioneer and Denon models, while the 1800 is about $500 less - perhaps a good enough reason to go with it.
At least that's how it is in my part of town.
I believe the 3808CI and 94THX (and RX-V3800) give you 2 video zones and 3 audio, while the RX-V-1800 has just 1 video zone and 3 audio. Am still deciding between those models myself.