I'm not exactly sure about stock, but for index fund, they said vanguard has competitive low expense ratio.

while Fidelity has various funds to choice from and also relative low expense ratio.

While both Vanguard and Fidelity are good brokerage firms/mutual fund companies, that said Vanguard has lower expenses than it is from Fidelity.  Of course, there are many other firms and banks offer Roth IRA, you may do some research as well.  Here are links for the maintenance fee schedules for Vanguard and Fidelity:

https://flagship.vanguard.com/VGApp/hnw/content/AccountServ/Brokerage/ATSIntegrityValueContent.jsp

http://personal.fidelity.com/accounts/aong/roth_IRA_more.shtml.cvsr

看了以后怎么觉得Fidelity便宜啊。