The 665 is actually the most similar. But the 950 is the model that actually replaced the One. However it's quite a bit different. If you're ok with the price tag, the larger screen and lack of physical num keys, the 950 would certainly be a nice upgrade. The 665 would be more of a parallel move, or slight step down due to the smaller, non-touch screen.
Probably not a great idea to stick with Logitech long term since they have discontinued the entire Harmony line and are only in a support/maintenance role from here on out.
Probably not a great idea to stick with Logitech long term since they have discontinued the entire Harmony line and are only in a support/maintenance role from here on out.