I have both Sonos Arc and a pair of HomePods. I don't have Sonos Sub or Ones.
For stereo playback, HomePods sounds significantly better to me. The soundstage feels much bigger and I prefer the overall tone and balance.
For surround playback, I prefer Arc. With a dedicated center channel, dialog sounds more intelligible. HomePods is still fine, but not as intelligible.
While surround experience is subpar to just alright on both setup, Arc has much bigger sweet spot (still small) and more convincing Atmos effects.
Practically speaking, Sonos is more versatile than HomePods, largely because it has eARC HDMI port. It can work with far wider range of contents.
Having said that, if I were to do it again, I would go with JBL 9.1. It is among the best performing soundbar out there, with support for wider range of codecs. If you are on a budget, upcoming JBL 5.0 MultiBeam sounds very promising.