How Do Unit Counters Shape Competitive Balance in RTS Games

[Battlemind]

I believe understanding unit counters is very important in RTS games. Hard counters like anti-air vs. aircraft create balance, while soft counters allow strategic flexibility. How do you feel about strict counter systems versus adaptable unit interactions? Do you prefer games with rigid balance (e.g., StarCraft) or ones with more fluid counters (e.g., Age of Empires)?