The forest is a better place for survival because the trees provide shelter and you can use branches and leaves and moss to make a better shelter. Also there are many different edible plants and if it rains the plants will catch water. If you gather enough you can get a clean drink of water.
I believe that a prairie would be a better place for survival because you are on more level terrain and in a more open area with a better chance of rescue by being more visible. Also there is less foliage therefore less likely for poisonous animals to hide and not be seen along with less chance of walking into a thorn bush or something poisonous. EX. Poison Ivy, Poison Oak, spiders
You say that you can see animals and dangers easier but doesn't that mean they can see you?
There also isn't that much food or edible plants to find, and with being more in the open it would be harder to hunt.
in a forest it is a lot harder to have even a slight idea of the terrain let alone what you might face. They say animals are more scared of us than we are of them but if they think you are threatening their young they will not hesitate (in most cases) to rush into defending their young ones lives.
Also you eat the wrong thing and you are poisoned or dead.