It sort of depends upon your needs, uses and preferences.
70D has a much more advanced AF system than the 6D. 19-points, all cross type vs 11-points with only the center one cross-type. Both are more than adequate for fairly sedate portrait shooting, but for other things, particularly any sports/action, the 70D might be better. 70D also has "better" Live View focusing (which we'll probably see implemented on 5DIV). However, the 6D's AF is able to focus in lower light... about 2EV lower than 70D, which complements the 6D's higher usable ISO/low light shooting capabilities.
Personally I like my 24-70/2.8 for portraiture much better on one of my crop sensor cameras, than on my full frame camera. To me, 70mm is only marginally "long enough" on full frame. I do like the FF camera for portraits, but use it for those with 85mm, 70-200/2.8 and 135/2 lenses a whole lot more than with my 24-70.
Not sure what you think the 6D will do for your portraits and general photography, that 70D isn't already doing. Unless you make really large prints (or crop a lot), and unless you like to shoot in low light situations a lot... not sure I'd bother with the FF camera. Sure, you'll see a difference between FF vs crop sensor images if viewing them at 100% on your computer... But that's equivalent to making a five foot wide print and then viewing it from 18" away. This is not a "typical" use of an image or way of viewing it. If you make prints more reasonable sized (8x10, 11x14, even 16x20) you will see little, if any difference. If you post and share images online or use them to illustrate a website, you will see no difference at Internet resolutions and reasonable sizes. Either camera is perfectly capable of making magazine cover size and quality images.
I think a lot of people buy into FF just because of all the hype.... and because they are in the habit of viewing their images overly critically on their computer monitor, at utterly ridiculously high magnifications.