I would highly recommend using fresh Thai red chillies (the smaller variety) if you can find them. They deliver that flaming red color and leave behind that spicy tingle on the tongue, usually associated with Asian sweet chilli sauce. Thai red chillies are spicy though, so be careful.
For traditional recipes that call for paprika, it's best to use what the recipe calls for, as the paprika is there for a reason, and its flavor and color are intended to give the dish an overall flavor profile and aspect that substitutions can't add.