Hi Elisha, as far as I know tiles should preferably be square.
They should be large for GPU and small for CPU.
Furthermore they should ideally fit in the image resolution, so for a 1920 by 1080 resolution, which is 16*120 by 9*120, you could use tiles of size 120*120 (for GPU rendering!), or 24*24 (for CPU rendering)
The ideal size does depend on your GPU, but the above rules should be followed for the best results.
You could also just use the Render: Auto Tile Size Addon, that comes with Blender. (I am not sure if it also considers what GPU you have…)
