The ultimate integrated amp.

What is ultimate to one may not be to someone else and "ultimate" to me means price no object; I suspect there are some extravagant integrated amps I haven't heard of.

All that said, if cost doesn't matter I'd like to have a VAC Phi Beta if for nothing more than to stare at!

At more reasonable prices, Hbarrel gave a nice list and I'll add to that the Musical Fidelity kW500, I am biased though, that is what I use; consider Audio Note as well.

I'll say it again.
The Sugden Masterclass Integrated.
I can't imagine any Amp, at any cost, sounding better.

They don't advertise, so they are ignored by the Hi-Fi Press.

Tube Research Labs has a new 225 watt a channel integrated that is now available-the ST 225. It is $5500.

TRL makes SOTA very expensive tube preamps and amps($100K+)
They are very excited about this new product.
I had them mod my MF A300 with great results and will get to hear the ST 225 later this month as a friend of mine is going to demo it with his Soundlabs.

Don't know your price range, but this may be something to look into.