I don't know what NW does, but CO is tough on giving out EQMs. For many discount NW (and DL) fares on NW operated flights I only get 50% EQMs, even if CO is listing the NW flight as a CO code-share, and I booked it on continental.com. The only way to get 100% EQMs for discount CO fares on CO operated planes is to book on continental.com.

You may need to factor the EQM earning rules into your decision.