Listening to: Pepper Adams - Encounter! // Nick Brignola - Raincheck // Serge Chaloff - Blue Serge
Clash for a Continent had stickers on thin wooden counters:
Hold the Line had die-cut counters, with improved art:
Note that CfaC was essentially the equivalent of both HtL and the HtL expansion, French and Indian Wars, combined. If you can get CfaC at a good price, I'd say go for it. You could probably pick up For Honor and Glory: War of 1812 Land and Naval Battles too, and that stuff would match what you get in Clash.
If what you're after is strictly play value, there's no real difference worth worrying about.