I'm planning to travel to the Netherlands, Spain and Bulgaria. My longest stay will probably be in Bulgaria. Now, Bulgaria doesn't issue a Schengen visa but allows people with a Schengen visa to visit. Which visa should I be applying for? Bulgarian Visa AND Schengen visa or just the Schengen visa for Netherlands or Spain?
The way I see this, you will need a Schengen visa in any case and therefore need to apply for one either from Spain or the Netherlands following the usual rules. The fact that you are also going to Bulgaria does not change that and Bulgaria obviously isn't the country where you are staying the longest within the Schengen area. And once you have a Schengen visa, I don't see any point in getting a Bulgarian one as well (provided you satisfy all relevant rules as far as Bulgaria is concerned – I assume this could mean staying less than X days, not working, having sufficient means, documentation of your return trip, etc.).
On the other hand, IANAL and I never went to Bulgaria on a Schengen visa so I have no personal experience to report.