I have an A7S and A7R II. Although I'm not a videographer, my choice (solely for convenience) would be the A7S II. I find the A7R II great for 4K video capture and couldn't see myself lugging around a recorder simply to use the A7S in the same capacity.
Let me 1st state I'm coming from a Canon environment and have a whole lot of Canon lenses...
I use the A7R, A7S, A7 II and A7R II with both Sony and Canon glass; the Canon glass using Metabones III/IV adapters. Both work very well; however, I do prefer the Canon image quality. I've also found Canon lenses of Sony quality or better are probably less (sometimes a lot less) expensive.
Don't forget about all the legacy glass available that can be adapted to the Sony A7 series cameras; Canon FD, Pentax, Minolta, Sony A, M42, T2 and just recently Nikon.
There are adapters available to connect almost lenses in existence to e-mount. I use Canon EF & FD, Pentax, Minolta, M42, T2, Tamron, Sigma & Nikon lenses w/ both the A7R and A7S. Most of the electronic lens also have automatic adapters.
You don't have to get the very expensive Metabones adapter. King, Commlite, Viltrox and several other manufacturers make equivalent or better adapters for considerably less $$$'s. I prefer the King adapter; nice fit and automatic. The Commlite allows me to use filters between the adapter and an EF lens.