* Apparent Brightness: If you're talking about which star appears brightest from Earth, that would be Sirius. It's a binary star system in the constellation Canis Major.

* Absolute Brightness: If you're talking about which star is inherently the brightest, meaning it emits the most light, then it's R136a1. It's a massive blue supergiant star in the Tarantula Nebula, and it's about 8.7 million times more luminous than our Sun!

So, it depends on your perspective!