The pros and cons of both motherboards are honestly just for looks as they are both B chipsets, but getting the 1070ti than the rx590 you will get more performance although it is only 8gb of ram, the rx590 only performs kinda just like a 1070, and a 1070ti when oc'ed is basically a 1080. 8gb is still sufficient, just upgrade later down the road, but do upgrade quick as ryzen likes dual channel speeds.
edit: A gtx1070ti doesnt need to be upgraded as quick as a rx590 (which is only a rx580 oc'ed)
edit edit lol: you may want to consider the r5 2600 with the x, you can still overclock the 2600 to the performance of the 2600x, but only get the 2600 if the price diff is like 50 bucks or more(and spend it on ram) if its just like 10 dollars more for the 2600x then just stick with the 2600x.