I have used Walgreens for several years. Tried Walmart in 2009 on a trip to Alaska as there wasn't a Walgreens there at that time. The difference was Walmart has to transfer your prescription to the local store to fill it while Walgreens keeps your prescription on a central database and can be filled by any local store. You can go online with Walgreens and find a store near where you'll be a few days down the road, launch the refill order to that store, set the date of pickup, and then get it as you pass through.
Unfortunately for me, Walgreens had a falling out with Express Scripts used by my insurance so I now have to have Express Scripts fill my prescriptions, but at least they do 3 mo orders easily and send email notices, so hasn't caused any issue so far.
