Last I checked the UltraAnalog 20400 DAC module (not a chip) and the Sonic Frontiers DAC came out some 30 years ago. They probably sound great but I'd be very hesitant to buy one today due to age and repair-ability.
I find R2R DACs to be 'relaxing' as in soft, smooth, slightly rich, a tad bit rolled off, but not very detailed or transparent. In this case, my vote goes for the Denafrips Ares series. To be honest, it was nice with 'simple music' but fell apart and got a little congested with more complex tunes.
P.S. If the DAC will ever be used over USB to a computer, music server, or network streamer, I would avoid anything over about 10 years old.
