The best format depends on the job. A favicon pack can include several formats without forcing one file to serve every browser and device.
ICO: several small images in one file
ICO is an icon container, traditionally used for browser favicons and Windows icons. It can store multiple sizes in a single file, allowing software to choose an appropriate frame. Favicon Studio’s default ICO contains PNG-encoded 16, 32, and 48 px frames. This is a genuine ICO container rather than a PNG with a renamed extension.
PNG: predictable raster output
PNG supports alpha transparency and is a practical choice for touch icons, web app manifest icons, and explicit high-resolution favicon declarations. Each image has a fixed pixel size. It cannot recover detail when enlarged, so start with a sufficiently large original or vector source.
SVG: scalable source artwork
SVG describes shapes rather than a fixed pixel grid. It is useful for source logos and supported browser icon contexts. Support and treatment differ across platforms, so provide raster fallbacks where needed. A tiny view can still be unclear if the vector artwork contains too much detail.
A practical combination
Keep your editable source as SVG if that is how your logo was designed. Generate an ICO fallback and the required PNG sizes for your website. Use an SVG favicon only after checking the platforms and search surfaces you target. Google’s current favicon documentation lists its supported image formats; do not assume every browser capability is also a search capability.
Transparency and JPG
PNG, SVG, and suitable ICO frames can preserve transparency. JPG cannot. This tool fills transparent areas with white when exporting JPG, which can be useful for previews but is usually not the first choice for a website favicon.
References: MDN image formats and Google supported favicon formats.