I just picked up a car from National today and drove to the city. I'm also a bit surprised about all the negative impressions. To me it felt no different from other old european cities. I've driven in Paris, Copenhagen and Milan to name a few and had no issue so far in Edinburgh. I'm parked about 100ft from where the Royal Mile starts. Maybe traffic is worse earlier in the day, but at 7pm it was quiet and Google maps got me where I wanted to go, took about 25 minutes from the airport.

The reason I wanted to pick the car up today and drive to the city was because, well obviously I flew in, but also I'm driving to the Highlands tomorrow and want to spend the little time I have before that exploring the city. This way I was able to leave most of my stuff in the car and it's packed and ready to go tomorrow when I need to leave and I can focus on other stuff.

Parking I imagine can be an issue and I'd recommend looking for a lot/garage beforehand. Having done that, I'm happy with my decision.

As for rental locations, I use National in the US so I picked that and it worked great. Good service at the airport lot and got a new Mercedes midsize SUV (had booked an SUV, "Volvo XC60 or similar"). Most city locations didn't even offer pickup, it doesn't seem like anyone wants to rent a car within the city and that makes sense.
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