National is currently having a status match that if you act now, you can get any hotel, airline, or another Car Rental agency matched to Emerald Executive Club.

Note: You already get Executive Club if you have the Amex Platinum or Chase Sapphire Reserve card. So if you do have one of the aforementioned cards, the only reason you would try this is to obtain Executive Elite Status.

There isn't a large difference as both get access to the valuable Emerald Aisle, where you can pick any car. During my Miami trip, I was able to get a Dodge Challenger (that I scratched) in the aisle. 

Reportedly you can get Executive Elite matching with Hilton Gold or Diamond. Even more interesting is that the Amex Platinum card comes with automatic Hilton Gold Status.

So, just by having an Amex Platinum, you can get National's Executive Elite status. 

Here are more details of what you get with Executive and Executive Elite

You can access the match page here.