Unless someone has a truly exotic option in mind (‘truly exotic’ in the sense of doing mass->energy conversions at rates well beyond the ones we think the laws of physics allow, or building pet wormholes into the universe next door to extract their energy or something; ‘reliable fusion generators now available at harbor freight prices’ would count as mundane in this context); you pretty much have to go to the sun if you want to keep up with the Kardashevs.
It’s simply where the mass is. The fact that it’s also already functioning as a gravity contained fusion device is a nice plus; but even if you had the technology to sidestep that requirement there would still be no getting around the fact that nothing else remotely nearby is nearly as massive.
