Back in the day when I used to rent a lot National was (just about) always the best for one ways. I don't know how they are these days.
One way from an enterprise local location?
1. AFAIK officially they don't do one ways. (I think some places do regionally)
2. the only way that'll be worth it is if the distance is not so far and you have the car for a while. for example: Recently, I was looking into a minivan one way from NY > BOS, keeping it for 2 weeks. most places wanted at least $750/week. I made a regular reservation by enterprise (probably $350/week) and asked what the penalty would be if I returned it elsewhere, IIRC they said $150 + .25/mile (to where I dropped it off, not miles driven) -I don't remember the exact numbers but it was something like that.
In that scenario (2 week rental, 250 miles away) it would've been much, much cheaper using enterprise, but when you're talking about 1000+ miles and only a few days I don't know...