Logo - Best saving option from illustrator to Adobe Portfolio?

Unfortunately, Portfolio doesn't support vector graphics at this time. 

The best you can do is upload a pixel-based raster.

Unless it contains transparent regions, you don't need PNG or GIF. 

A JPG optimized for the web will produce more than adequate results on a web page.

See below for Portfolio's recommended image file size and dimensions.  Keep in mind that lots of large image files causes slower loading web pages.  For this reason, I try to keep Cover images under 100KB. 

https://help.myportfolio.com/hc/articles/360038360914-Formatting-Images

Hope that helps.

The best choice of pixel-based file format depends on the nature of the logo. JPEG would be best for photo-like material or imagery that has a lot of texture or other details. PNG is much better for more graphical images that have flat areas of color. The data compression method is more efficient for that kind of detail. Plus, broad areas of flat color will stay "clean" looking. JPEG can introduce macro-blocking artifacts, "mosquito noise" and other issues into such imagery. I think people only use GIF anymore for looping animations.