Linear, because there is a constant interval (difference) between the x and between the y values. The function is also rational because it can be defined as the quotient of two functions of x.
[The standard form is y=mx+c (y=-2x+5, which could be written y=f(x)/g(x)=(2x-5)/-1, for example, where f(x)=2x-5 and g(x)=-1.)]