I would probably go with:
Bishop England @ Hilton Head - #1 2A/1A team in the state versus a highly-skilled 3A team. HH's only real challenge until the state playoffs.
Mauldin @ Riverside - History & proximity. The most successful upperstate 4A program versus the most successful upperstate 3A program.
Dorman @ Dutch Fork - Late season match has two 4A teams that may be ranked in the Top 5 of the state poll. Upperstate vs. Lowerstate.