This is an external airport gateway: Toulouse–Blagnac Airport (France, gateway to Andorra) is in France, not Andorra. The rental contract must permit the onward international journey and every transit country.
TLS is in France. Compare a cross-border rental with an airport transfer to Andorra, confirm permission for every transit country and check winter equipment before leaving the branch.
Toulouse Airport publishes its on-airport rental operators. Follow the voucher for the specific branch, vehicle area and return entrance. Explicitly book permission for Andorra and any Spanish transit; a French airport-labelled offer does not establish cross-border cover.
A car can be useful for several valleys, mountain accommodation and flexible touring beyond Andorra la Vella. For a single resort stay, compare an airport transfer and local transport. Include parking and winter equipment in the decision instead of treating the small size of the country as proof that every drive is simple.
Compare airport collection with a later collection if you start with a city stay. Include the transport to a different rental branch and any extra parking nights when comparing the total cost.