I think they are all pretty close to each other in terms of services and cost. One may require slightly more in postage deposit than another, but we are not talking about huge amounts of money.
I think the biggest factor in your decision may (should) be the location of each company *if* you decide to go get your driver's license. Your Best Address (what I used) is located on the East side of SD (Sioux Falls to be exact), while some others (like America's Mailbox) are on the western side of SD near Rapid City. This means I could have saved myself some fuel costs since I was coming from Colorado. Plus, there are some cool things (National Parks and such) to go visit near Rapid City, not as much near Sioux Falls
If you must stay for 30 days (required to get your concealed carry permit) you are required to stay in the same county as your address. I have found that to be a little troublesome as Minniehaha County (Your Best Address) is very small and there are very few RV parks and those are priced very expensively for most of the year. I do not know how that compares to Rapid City area but something worth researching if you have a CCP and want one from SD so all your addresses match on all your paperwork.
Larry from YBA was very, very, very nice and walked me through all the paperwork over the phone (standard service) and made sure everything went smoothly. I have no problems recommending them. You can tell them that I referred you and I get some free month(s); I am box #936.