issue with AMD Demon floor pan..please help newbie

i haven been playing arond with the doors, changed the pins and got them lined up. they look much better now, no porblems with gaps so i think im ready to weld.
i have to buy a bottle of mig gas. now i have heard the bestfor sheet metal is c-25 but is there anything better. i have been told that "mig gas gold" is the best. which is 90% argon 10 co2. would that be a better choice?