I was just flying down from the mountain to find some oily rocks with my griffin and then a giga spawned right in front of us. That's one heck of an experience. I tried to kite it with darts but it just keeps running away and then I saw another one. Everyday, Ark will make you poop.
If one is encountered near water, you can simply lure it out to sea with a flyer and it will swiftly drown. Given the water is deep enough. If encountered inland not near water. Pray to the overseers you have something fast enough to out run it. Then promptly die because they're as fast as a mad Hispanic mother with a shoe. Not as deadly as one though.