There are tone of choices you couldmake and none would be wrong. each offers somthing diffrent. some last longer, some look better on certain colours. Like anything its a personal choice.
i would recomed either looking into duragloss 105. this stuff works awsome. Give good looks and lasts a long time. and to bootits cheap.
the other one i like is wolf gang
deep gloss sealent. it gives awsome results. it makes colours really pop. i think it would look great on your mustang. howevr it only lasts 3-6 months depending on condtions.
The choice is up to you but those are the 2 i would recomened looking into.
ohh yeah try 2 or 3 coars before applying the wax to add protection and add to the look