From personal experience, a pixel 2 is significantly faster and smoother than a pixel 1, and the internet suggests the 670 chip in the 3a is slightly faster for general use than the 835 in the pixel 2, though for gaming its somewhere b/w pixel 1 and 2 as the 670 GPU is b/w the 821 and 835.

So for normal use, its definitely a upgrade to a pixel 1, and a slight upgrade over the pixel 2.