I'd get the SuperNOVA G3 550W because it's fully-modular, made by Super Flower, has a 7-year warranty, and will be up to the task when I upgrade my GPU to a GTX 1070 - 1080 - 1080 Ti in the future. This would be my first choice.
The Seasonic G 550 is also good, but it is semi-modular, made by Seasonic themselves, and has a 5-year warranty. That would be my second choice.