If you have a porch with a northern exposure, up high behind the eve and away from the house wall is best. That way it's less likely to be influenced by the house wall temperature, and sheltered from sun and rain except when they go horizontal.

I have 2 outdoor sensors: one is La Crosse and the other is Acu-Rite. They're mounted within inches of each other and the AcuRite is always about 3-4 degrees lower. I've used an IR non-contact thermometer as a 3rd reference and the AcuRite is the more accurate of the two. (They're probably all made in the same factory in China.)

I don't even bother with wind -- my Lacrosse wind sensor bit the dust during Hurricane Sandy, but I always thought of it as a low-quality toy compared with the Raymarine sensor on the boat. It's more than I want to spend to get accurate wind in a home weather station, and I'm satisfied to get online readings from an airport station about 6 miles way. But on the boat it's way more important to know speed/direction right where we are now.