Toxic Orb does less damage to Swellow the first two turns it is out, but on the third turn, it is tied with Flame Orb for total damage done. If you think you can keep Swellow in for more than three turns, you'll want to use Flame Orb, otherwise, use Toxic Orb.
You better win. D:< lol
I'm getting ready to go out. My lizard needs crickets.
If you're not here when I get back, hopefully I'll talk to you later tonight. :3