2 things:
1) Hertz does not reward number of days. They award points per $ spent. If your company has low negotiated rates, it will take you a LONG time to get enough points for a free anything. National rewards by number of days, 1 credit each for rentals within various buckets.
2) Point redemption is not an apples-to-apples comparison. Any of National's free days can be used for expensive one-ways. Hertz points for one-ways are typically double the thresholds for roundtrip. Avis points can theoretically be used for one-ways, but with no published standards.