Rear mount.
It all depends on the market and company structure. If you have enough guys on the crew to drive the other chip vehicle, etc. I'm sure there are operations out there that would rather have a rear mount than a forestry, but logistical issues require that they consolidate drivers/vehicles and end up needing a forestry.
A rear mount makes sense if the man power is there. You can keep working if the chip truck needs to be unloaded. You'll most likely access more with a rear mount, and have a bit less ground pressure. A bit more visibility when backing up without the dump body there in the mirror. Set up may even be easier depending on the site, making for more efficient processing of material. Plenty of room for plywood/mats, etc...
We pretty much need 4x4 capabilities where we dump chips, and the forestry truck will easily get stuck on a bad day. The chip trucks are 4x4 so it's all good.