Personally I ask for the $ECV.

My primary paid flights are DFW-LAX so there are several reasons the $denominated voucher is better for me.

1.) This market does not require any minimum stay ie: same day return allowed and NO sat night stay required

2.) I can earn miles with the ECV purchased ticket and there are alot of miles earned on this route.

3.) the fare has ranged from $150 to $219 for the past year, so whether I get $200 or $300 I still have at least one free R/T, that I earn around 13,000 miles on.

4.) If I am not going to LAX I generally am taking a weekend trip, so the Sat night stay is not a problem.

5.) All my travel is at my expense so I prefer to be able to earn miles so that I can continue to maintain Plat.

6.) For non elites or elites on Partner airlines W can be a hard class to find availability in.

You generally have the option of either a free R/T on NW metal, or a $ denominated ECV. The dollar amount is generally determined by the time before the next flight. I believe the cut off is 3 hours, but it might be 4 hours.

So if you get bumped and wait less than 3-4 hours for the next flight the compensation will be a free ticket OR $200 voucher, if it is 3-4 hours or greater you can choose either a free ticket or the $300 voucher. If it is overnight on Intl flights it can be either $700 or $1000 again depending on time of the next flight.