Do you have AWD/FWD? Since rain is your main concern, you should be looking for good all-season tires, then you don't have to change your wheel/tire setup any time of year, unless you like running ultra high performance summer tires at any point.
Tirerack.com has a ratings guide that is fairly accurate, and that would be a good start. http://www.tirerack.com/tires/SelectTireSize.jsp?autoMake=Ford&autoModel=Edge+Sport&autoYear=2013&autoModClar=AWD
Also, http://www.tirerack.com/tires/surveyresults/surveydisplay.jsp?type=CSTAS
Whatever size of wheel you choose, you have to choose the appropriate tire to maintain the various aspect ratios. Tirerrack will point that out also, if you input your vehicle. If you want a tire sizing calculator, http://www.miata.net/garage/tirecalc.html is one of the popular sites used.
HTH.