"Upgrade"
Both guns are in production- its not a matter of Gens. The virtus is more flexible with 3rd party cans but at the cost of weight.
The Spear is more like a mass issued rifle - sorta like an M4A1. Lighter weight, simpler gas adjustments. The problem is you're pretty much limited to flow-through Sig cans.
While everyone is in the panic state of "oh no the Gen 3 is here" and offloading them at stupid prices, I would get a Virtus, especially while the bendy barrel issues are getting resolved. I would highly recommend a W-TAP serial number as they have, IMHO, better features: chrome lined barrels and milspec (non comp) triggers