Capitalize strings in sed or awk

I have three types of strings that I'd like to capitalize in a bash script. I figured sed/awk would be my best bet, but I'm not sure. What's the best way given the following requirements?

1. single word
   e.g. taco -> Taco

2. multiple words separated by hyphens
   e.g. my-fish-tacos -> My-Fish-Tacos

3. multiple words separated by underscores
   e.g. my_fish_tacos -> My_Fish_Tacos