Which engine is best and fuel economy

I am looking into used 12 passenger Expresses and Savanas which is when a friend told me the late 1990s ones have a Chevy 350 variant as an engine option. Would that be a good choice since I assume the V6 is a snail and the Diesel is not economically sensible for what I am doing. For highway driving is there a certain sweet spot where you can get pretty good mileage?

I am looking into G20s and Vanduras as well as Ford Econolines because I am not sure which is the better or best Van, but people keep telling me to avoid the Dodge Ram Vans like the plague.

Usually I hang out in the Chrysler Minivan forum, but not sure how much longer mine will last.