Walmart I would apply in store, since your identity can be verified right then and there if there is any issues, and also if you spend $100+ you get $20 off. For me it is easier to spend $100 in the store than it is on walmart.com so that is 1 plus.
The other two I wouldn't think there is a big difference. Same thing if you apply in branch for chase freedom, they can verify your identity, but unless you have a large deposit account with them the banker won't really be able to help you with anything.
Apply in a branch for chase freedom. Apply on the phone for discover.
Whats the difference applying in branch or on the phone with Chase?