American vs Northwest. Also - ff miles vs. free car rental

[jjww]

I rent multi-monthly with National, so I earn 50 ff miles per day.

I'm leaving Delta, as they are charging 50 cents per day.

Will have my miles begin to go to either American or Northwest.

My trips the last few years have been :

Las Vegas to Chicago
LV to Green Bay
LV to Philadelphia.

Future flights will probably be to those same areas - perhaps instead of Philadelphia instead a NY airport or Newark NJ or Wash. DC.

Eager for any opinions on which program is preferable.
Last minute question - may have to make choice Friday early afternoon.

Thank you.



Related to my question above re: American vs. Northwest -

I just read an article stating that one should use FF miles rather than save them.


A corollary to this would seem to be that if one has a choice of something of similar value, to pass on the FF miles.

If I value the FF miles at 2 cents per mile, they are worth slightly more than my free car rental days option.
But it's close, and will be closer or perhaps even in 6 months when the cost of my car rental days will increase (so free days will be worth more).

Any opinions on this - taking credits towards free auto rental days as opposed to starting an FF account with either American or Northwest???