As Terran
Make:
Siege Tank
Widow Mine
MedivacSplash and better positioning beat raw Marine count.
Open in the counter tool with Marine tagged ->As Protoss
Make:
Colossus
Disruptor
High TemplarForce Marines to split, then attack while stim is wearing off.
Open in the counter tool with Marine tagged ->As Zerg
Make:
Baneling
Lurker
InfestorCreep and surrounds matter as much as the counter unit.
Open in the counter tool with Marine tagged ->
Marauder
Reaper
Hellion
Hellbat
Cyclone
Thor
Viking