Totally agree with Willi on this. If you can use Illustrator to create the original logo, even if it is for web. This will keep the original file as vector and will make your life a lot easier going forward for printing and updates, etc. If you can use Illustrator then create it and export either a .PNG or .SVG or both, use the .SVG and have the .PNG as the fall-back. This is good practice. .PNG is what you want as it carries transparency, I would steer well clear of .JPEG if you can as you will always lose clarity due the the lossy compression that's comes with .JPEG format. All the best.
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