Same issue where I work
however I initially was budget but the service was horrendous. starting with the buses, they just seem to be slower at every airport that I traverse.
I could look past the issue of not earning any FF benefits with budget (per company contract) and for Avis we could get FF Benefits..
however I had too many issues with budget, it was too difficult to get resolved so I have been with Avis for a few years now and its light years better. Factor in the FF benefits I now earn and its great
like you I'm exec at National too so I use that for personal travel.