I have ridden both coasters in question, and there is no doubt in my mind Mamba is the better of the two. Contrary to what Dustijn says, I think Steel Force's second hill is significantly *slower* than Mamba's. I get air the entire way down in the front car on Mamba, whereas Steel Force I barely even leave the seat.
Mamba's helix is far superior to Steel Force's also, IMO.
The only thing I think SF has on Mamba is two tunnels and better bunny hops on the way back home. Other than that, I think Mamba is the superior ride.
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"Yes if by crestfallen you mean KILL US!" -- Homer J. Simpson