To gauge the quality of skin tones reproduction, you need a photo that is properly exposed for it. With all due respect, I don't think the photo Emil linked to gives a fair assessment of E100VS, so here is an example from my archives.
This is using an AI Nikkor 105mm f/2.5 around f/2.8 or f/4 on a blazingly sunny day around noon. We were on a boat, so there's lots of UV around. Nevertheless, it worked like a charm. The wide aperture probably helped reduce the contrast a little bit.
Here is a 100% detail from the scan. You will notice as mentioned above a slight redness, but to me this is more because of the scan than the slide itself. When viewed with a loupe, the slide is very neutral.
Ektachrome 100G is also a valid option for portraits, although it can render certain features a little bit pasty. Here's a sample taken with studio strobes on a Super-Multi-Coated Takumar 135mm f/3.5 around f/11 or f/16.
Here's a 100% detail of the scan. Damn that Takumar lens could be sharp! E100GX could have done a slightly better job at giving colour to those features. The exact balance of the scan could be in cause as well.
But for the best skin tones, I prefer to go negative. My favourite film for it is Portra 400NC. Here's an example taken with a Mamiya C330 with 105mm DS f/3.5 around f/8 probably:
Did I say that the 105mm DS was sharp?
The thing I like about Portra is that it makes people alive, while still doing a great job at rendering landscape colours. What's more, it's great for any skin tone. Again, using the AI Nikkor 105mm at wide apertures:
So if you go for slide film, your best bet with Kodak would be E100G/X, but E100VS is a valid choice insofar as the saturation is useful to your pictures.
In the Fuji products, the only slide I've used on skin is Provia 400X. It's very nice, but so damn expensive. At any rate, if you intend to do serious portrait work go for Portra NC, or perhaps the Fuji equivalent. I have a beef with Fuji's colours, so for now I stick to Kodak for almost everything colour.