If I could only have three devices, I'd go with what gives me the most utility and power. My choices are basically what will limit me the absolute least and provide the most additional options for anything that may come my way. Seems like a pretty easy decision -
1. Mac Pro 5,1 - 12 core (can literally expand to anything I need, tons of storage, more PCI options, tons of ram, etc.) for basically anything I can throw at it.
2. Macbook Pro - probably a late 2011 model - (discrete graphics a big plus, optical drive, sd card, usb, thunderbolt, ethernet, and firewire, along with the quad i7 and also tons of ram for cheap) - has the most utility in a portable format, for traveling or mobile location jobs.
3. LG V10, or really any decent Android phone - (Great camera, much better experience syncing with OSX than the iPhone, way more friendly with transfers and bluetooth syncs with other phones than the iPhone, runs any app I need it too, can swap batteries on the go, expandable storage via microSD, can use my micro USB flash drive as an emergency dump of storage, and after having a phone with an IR blaster, I don't think I could ever go back.)