[davismwfl]

Neither would hurt your career later, but the startup may be harder to work at and complete a PhD.

A lot will depend on the startup and your goals personally, but neither will hurt you. I do see pros and cons on both sides, and I would personally say for your goal it might make better sense to go with the larger retail business. For businesses like Google/Amazon etc, they all do things at a very large scale and likely anything that helps prepare you to think in those terms is the better choice.

Good luck!