For Escapees your mailing address is Texas. But you also have the option to choose a domicile (physical address) in Florida or South Dakota, in which case you will have two addresses, one in Texas and one in your chosen domicile state. So the three options are:
1) Texas address only
2) Florida and Texas addresses
3) South Dakota and Texas addresses
The cost of the three options is the same as long as your mail is sent to Texas, otherwise you have to pay $1 extra per envelope if mail is sent to either Florida or South Dakota (because they then forward to Texas).
We decided to go with the Florida and Texas option. We currently live in North Carolina, so it's much easier for us to go to Florida to get our driver's licenses than it would be to go all the way to Texas. (We are also good friends with Minnie and Mickey, and by being Florida residents we get discounts on park tickets). Once we get our driver's licenses in Florida and move out of North Carolina, we will no longer have to pay state taxes. Other reasons you might choose one of the three states over the other two is for vehicle insurance rates, vehicle registration costs and inspection requirements, and health insurance rates.
We just started using Escapees and are new to this, so please double check this information and forgive me if I stated something that is incorrect. When you call them they are always friendly and helpful. We are going down at the end of the month to get our driver's license, library card, and register to vote.
Another option is St. Brendan's Isle in Florida, which is similar to Escapees but only have an office in Florida.