Tough Call...
I love both Wild Thing & Mamba. Wild Thing has that amazing airtime on the 2nd hill (supposedly the longest airtime of any coaster, anywhere), and Mamba has that awesome helix, and slightly better airtime on the bunny hops on the 2nd half. WoF also has Timber Wolf, which I thought was great ! I got some serious air time throughout the ride. The trains have seatbelts, and therefore the ride ops don't seem to care much if you leave your lapbar loose. I think Timber Wolf has the best air on any coaster I've ridden, at least in recent memory. Shifting the focus back to Valley Fair, they have an awesome S&S Power Tower, 2nd only to the one at Cedar Point.
So really, it's a tough, tough decision. It pretty much comes down to Wild Thing vs. Timber Wolf. If you are a big woodie fan, go to WoF + you'll still have a great steel coaster with Mamba...however, if you like free fall rides, and prefer steel to wood, then maybe Valleyfair! is the better choice.
I really had a great time at both parks, and I'm sure you'll enjoy it regardless of your decision.
(btw, if they have reduced their season pass prices the way that Cedar Point did, it might be in your best interest to get one. Who knows ? You might get the chance to visit the other park before the end of the season after all...maybe even Cedar Point too !)
*** This post was edited by Joe Carroll on 8/8/2001. ***