Posted 23 December 2014 - 04:01 PM
Always a level editor first.
Good game companies put significant resources into their content creation pipeline. It's one of the many areas in game dev where the initial cost of developing something will negate far bigger costs incurred down the road. Spending a month to save 5 minutes of work doesn't sound worthwhile until you realize that many people will be incurring that 5 minutes of work multiple times per day over the span of several years.
Note that there are pre-existing level editors. They might not be good fits for your game; a 70% fit is better than not having an editor at all, but good practice would be to put in the time and effort to get to a 100% fit before having anyone invest serious time into making your content.
You can make a Windows-only toolset easily enough in C# using Microsoft's GUI libraries, or a Qt app, or a wxWidgets toolset, or one based on HTML5 via Chromium Embedded Framework or Awesomium, or any of a number of other high-quality options. For smaller projects I'm a fan of building your editor right into the game. For larger projects, a separate editor that can embed the game support code into it works better.