What's better in a campaign: "Send from" from a sub- domain or from our real domain?

Hey,

In terms of bad reputation and best deliverability, What's better when sending out a campaign: "Send from" a sub-domain or from our real domain?

I'd like to hear what do you use when you send out marketing letters. What would you recommend? is it acceptable and recommended to revise the address of sender to our real domain?

Thanks!