Steady winds really aren't much of a challenge. All you need there is a plane that's fairly neutral handling so that cross winds don't flip it up on its side and enough straight line speed to push through the wind and still maintain a decent ground speed. Also, the faster you can fly the less effect the wind has on the plane's flight path and attitude overall. Nearly any traditional "sport" plane fits the bill there, with the sticks being at the top of many flyer's lists. For gusty days it gets tougher, because you have the problem of big gusts hitting the front of the plane and slowing it down, and also swirling turbulence causing unwanted rolls. For those, you need a small frontal area and wings on the short side (less leverage for the turbulence to push on). And again, you need speed. Once again, sticks do the job nicely, as do most of the "senior pattern" type planes.

On a windy day, I show up with a .60 size ultra stick and a .40 size Kaos. The stick is for tossing around and playing in the wind, while the Kaos is for working on flight skills. I know the OP is asking about park flyers, so the simple answer to the question would be the Mini Ultra Stick for probably 10 mph winds as a beginner flyer and upwards of 18-20 mph with more skill. Once you've got flying that plane down, the hands down best windy day park flyer on the market is the Parkzone Stryker. I've had mine out in gusty 30-40 mph winds before (as reported by the weatherman) and it just shook it's rear and kept on flying!