What you’re describing could correspond to any number of voting systems, depending on what you mean by “least popular” (which is, of course, the crux of the issue). If you read my previous post, there’s a rather detailed comparison of a bunch of voting systems with simulation results based on a model of voting behavior. And yes, tactical voting to some extent is inevitable, though its effectiveness can be minimized.

The point here is a bit more nuanced: it’s difficult to even think about the importance of tactical voting in voting systems where a non-tactical ballot isn’t even well-defined.