Hi ​@JonXB 

Welcome to the Sonos Community!

Wow - good question! My first instinct was to say I’d go for option 2 and have the additional immersion of having more channels at the back.

Though, the additional dialogue enhancement features of the Arc Ultra could certainly come in handy - some movies are just plain difficult to understand if not at actual cinema volumes!

And, due to the modularity and flexibility of Sonos systems, a later upgrade would be easier/cheaper if you started with Arc Ultra and the Era 100s - if you were open to a later upgrade (and don’t already have speakers in all you other rooms) the 100s could be moved to other rooms at a later date when Era 300s take over their duty.

So, I’m now thinking that if it was me, I’d choose option 1. Besides, newer is better!

But - and this is a biggie - as I have been working from home since COVID lockdown, I have not personally heard either the Arc nor the Arc Ultra in any configuration. So, I don’t consider myself quite qualified to say one way or the other - my posting here will bring this thread back on to the list of those recently active, happily,  and you may yet hear from someone who has experienced both setups, or close to it, and can advise.

If you do go for second-hand, I recommend using our official eBay stores so you can still get a warranty:

I hope this helps.

Sonos has convinced me I need the improved dialog the Ultra offers.

From what I've read the Sub gen 4 is the way to go with the Ultra so I may be needing to upgrade my gen 2 at some point.

I don't have a good room for the 300s but if I did I'd sure go with them over the 100s. I may get a pair anyway and if they just won't work in the TV room I'll put them where I have One SLs now and move them.