Greetings and hallucinations, treenail.
Fibreglas bodies have a nasty problem of disintegrating under sunlight. Metal does not. However, metal does have a very unnerving tendency to corrode. But that all depends on where the bus previously called home.
I purchased an 03 Thomas 84 passenger HDX from Midwest Transit
. There is some surface rust, but, overall, my Brunhilde is healthy. Some lots will sell you pristine vehicles and others will sell you cancerous wrecks. Midwest shows you pictures from a lot of aspects.
Your choices will be reflected by your needs, desires, and dreams. How much room do you need? Will you be a full-timer or a weekend warrior? Availability is pretty much defined by what you're seeking. Customization? The sky's the limit. Weight and cost are also determined by what you want and where the bus has been used/sold.