Who misleads people? Satan or Allah?
Let us look at Noble Verses 4:119-120 "[Satan says:] "I will mislead them, and I will create in them false desires; I will order them to slit the ears of cattle, and to deface the (fair) nature created by God." Whoever, forsaking God, takes satan for a friend, hath of a surety suffered a loss that is manifest.
Satan makes them promises, and creates in them false desires; but satan's promises are nothing but deception."
Let us look at Noble Verse 16:93 "If God so willed, He could make you all one people: But He leaves straying whom He pleases, and He guides whom He pleases: but ye shall certainly be called to account for all your actions."
There is no contradiction in the above Noble Verses !.
In the Noble Verses (4:119-120) above, Allah Almighty clearly tells us that Satan is the primary decieving force that we might face. For this reason, we must always avoid listening to Satan's temptations. In the Noble Verse (16:93) above, Allah Almighty helps whom ever He wants and leaves astray whom ever he wants. Depending on our intentions in this life, we might gain the love of GOD or gain His dislike or hate. Allah Almighty is not obligated to help everyone He creates. He gives us choices and makes the straight path to follow crystal clear for us. It is ultimately up to us (the humans) to make the decission of going with the path of Allah Almighty or go with the path of Satan and evil. See also 45:15.
This topic is further discussed in this site: Is Evil from Satan, Ourselves or Allah?