Nissen in Ireland
Mercedes in Italy
I have driven many rental cars in the United States and Canada. That seems easy. I have also driven them in Ireland, England, Scotland, Italy, Austria, Germany, Liechtenstein, Switzerland, Spain and Portugal. That is pretty easy too.
We use AutoEurope as our rental agent. They have always come through. No problems with them. As for driving in Europe, you need to read up on the laws and street signs before you go. Some are different. As for driving on the left, my copilot has always been helpful reminding me which lane after making a stop for lunch or petrol. The motorways like the Autobahn are not tricky. Just choose your speed and stay in that lane.
The roads are good in Europe. The drivers seem better than in the US and it may be that the roads often are more narrow and the speeds higher. The European drivers are very alert. They do honk their horns some, but they rarely carry guns or have road rage over little things. If you seek forgiveness, some countries have "Visitor" signs for your back window. (Not a good idea as it advertises that you have luggage to take.)
By auto you see more and stop when you like.