I suspect the question means more along the line of processor speed and memory, with the goal being trying to determine what is the equivalent experience. For instance, I have a Rku 2 XS, a Roku HDMI Streaming Stick, and a Roku 3. The Roku 3 is, by far, the most responsive. The menus load notably faster. The Roku Stick and Roku 2 XS are, it seems to me, roughly equivalent in speed and responsiveness, and, apart from the version of Netflix (2 XS has the old version, Stick has the current) the experience is similar. I prefer the Roku 3 (or Roku 2) experience.
And, if that's not a good reading of the question, consider it mine. To which Roku device is the experience most similar?
Roku Ultra (4660)
Apple TV (5th gen), TiVo
Roku boxes from every generation.
Apple TV (2nd, 3rd, 4th gen)