A Full-Frame sensor (35mm) is the gold standard for that "pro" look with blurry backgrounds and great low-light performance. APS-C is the "sweet spot" for hobbyists—smaller, cheaper, but still very powerful.
Don't get trapped by megapixels. High megapixels (45MP+) are for huge prints; lower megapixels (12-24MP) often mean better performance in the dark and faster shooting speeds. buy image sensor
Look for Back-Illuminated (BSI) or Stacked sensors. These are the modern tech specs that allow cameras to focus instantly and shoot without that weird "rolling shutter" distortion. A Full-Frame sensor (35mm) is the gold standard