Be aware there can be a cost difference if you want to provide SSL to your users. A wildcard SSL cert to cover *.app.com will cost you $200/year, whereas a sta

Be aware there can be a cost difference if you want to provide SSL to your users. A wildcard SSL cert to cover *.app.com will cost you $200/year, whereas a standard SSL cert to cover just app.com will cost you $20/year. I personally prefer subdomains, but I agree that people are generally comfortable with whatever approach you take.