Denali Park or Kenai Fjord Park?

Our cruised will be ended at Whitter. We will only stay two days one night in AK. I need some suggestion:

1. Which park is better? Denali Park or Kenai Fjord Park? Denali is 5.5 hours driving and Kenai is 2.5 hours driving. Denali is further than Kenai Fjord that is why we are struggle. We have parents and pregnant woman go with us. Or any other tour suggestion? 

2. Where to rent a car from Whitter? I found that car rental costs $450 for two days if we return the car to Anchorage. 

Thanks very much!