I made a little analysis for the existing network and what exit node would enhance it. Below you can see the exit nodes we have right now:
As you can see, all current exit nodes are in Western Europe with Laika being the only one in the east. I don't see another exit node in northern Europe to be very useful as Central, Eastern and Southern Europe would still be completely uncovered.
The exit node I propose is Romania (Bucharest). If you take a look at the EuroWeb
infrastructure, you can see what backbone they have.
Their own backbone goes all the way from Frankfurt to Turkey, covering Central, Eastern Europe and Turkey. They also have leased lines going all the way to Moscow, Helsinki and London. This essentially helps covering the area marked in the red circle (2nd image). The green area shows the backbone.
Romania has also very fast, cheap internet and a good infrastructure with fibre cables connection all major cities. This and the fact that there is no data retention law (it was ruled unconstitutional twice [2009; 2014]) makes it the best choice in my opinion.