Digi vs mRTK should be pretty similar for repeatability. Both cell based RTK. mRTK you wouldn't need the ipad or data plan and if you're running newer green equipment you'd already have the MTG in it to send/receive. 

SF-RTK is new enough....they've been testing it for 5 years or so it sounds and it's been good so far. I don't think anyone has used it long enough to know other than the JD developers. It's just SF3 on steroids and that's been pretty darn good.