I've used SiteLink and WebSelfStorage in the past, currently using Centershift Store. I'd rate them as #1 SiteLink, #2 WebSelfStorage, and a distant #3 Centershift Store.

There are many headaches with Store's functionality, such as it doesn't make change, so unless you are confident doing it in your head, you have a calculator by your keyboard, and it also won't let you enter a check for more then the amount of the payment. So if someone owes $77.07 and they mail you a check for $80.00, you enter the check payment in twice, once for $77.07 and then another payment for $2.93 (I did this today)...Store is ok, but it's all the little things it doesn't do or doesn't do right that drives me crazy.