Mine are 14's. Really depends on your rig and what you want to do with it. If you have a full bodied rig that is going to be more of a crawler, using more down travel and less up travel, 14's will be plenty. 16's and up I think are more suited on the front of bouncers and full buggies that desire more about half and half on up travel/down travel. Most people's **** has more clearance and room in the back for travel in all directions, so 16's and up work fantastic in the rear of mine. Lots of folks will say travel is overrated, but I've also been up a lot of **** real easy while others hang up and drag **** on. Long travel is overrated to an extent, but there's not one single negative thing to be said about having all 4 tires touching the ground when flexed out, instead of toting one because suspension travel was limited.
To really get the full use out of 16's in the front, you really gotta have all your clearances worked out. Hydraulic lines if full hydro steering have to be proper length to accommodate for the longest travel it will see and ran to where they won't snag anything while suspension moves, link clearance around the frame and the bottom of the engine, tires getting into the wheel well or axle hitting bump on up travel and still having up travel left in your shock (wasted travel). Angryfab cut and re-angled my front frame rails to clear my tie rods for full hydro, accommodating for more up travel. So my uneducated opinion would say the answer is 14's in your case. I almost went with 12's because I was worried about up travel and I have a lot of ground clearance, but I'm glad I went with 14's, they are perfect.