100% SVG. I’m not sure why I would go with pure CSS.
Really? I can think of about 10 use cases for this. At the BARE MINIMUM, it would be an awesome alternative for special campaign or whois site. The reason? You can do things CSS that you flat-out can’t do with SVG… at least without hand writing it.
3d transformations are DEFINITELY something that comes to mind. That is the one area where I feel CSS is superior for graphics. Now… I have seen software or plugins to create 3d SVGs on a canvas or whatever… but it always seems sluggish to me and I hate the idea of bringing JS into the mix for a logo.
I think for really high-end graphics intensive sites… there is a place for this.