What types of domain names are preferable or more reputable in any given countries?
I see a lot of campaigns running in Sweden or France, that uses .com domain names, and it looks like they are doing good if they can keep campaigns running for months.
Would you rather buy .eu for the whole europe or .se, .fr, .dk or any other specific country domain? Or just use .com for all the GEO's.
Domain name itself doesnt have a large impact on campaigns running on paid traffic, and the extension will have even lower impact, if any. Im running on .com domains in many GEOs and it doesnt seem to have any effect. I would expect the country specific domains to have some positive effect in case of offers that ship tangible products, so for example diet, skin care etc ... looking at this as a customer, I would probably trust a site in my own language on my own country's TLD more. I dont have any personal data on this, never tested this. I tested domain vs no-domain tho and it didnt have any impact, what helped was a domain name related to the country, tho it was still a .com 
Ok, I see. So for landing page it might not be that important.
Can only speak for Sweden but .com would be preferred over .eu for sure.
In Sweden we use .se, .nu or .com any of those would work best.
Can only speak for germany(Austria as well). .com, .net, .org are common like the local one .de/.at - no difference at all.
Some Websites are using .eu as well - people know it too