Softest, smoothest sounding capacitors you've tried?

V caps are very nice sounding caps. Quite expensive . 

Man what a loaded question! Power supply filter mundorf mundorf with PI CRC. Afe and vas really like kemet mkp wherever they fit. Vishay 18xx series mkp as well. Listening to my hafler 9500 with 100uf audio note /.1 uf mundorf mkp right before the output fets and man that combo is pretty special after about 40 hrs at high current... I know Solens don't get many accolades., but the mkps in my Dunlavy SM-1 x-overs I would never think to change. Flat neutral and oh so honest, so to answer the op, try Solen mkp. They may very well fit the bill.

Duelunds

For mainstream audiophile stuff I use MIT styrene and tin foil from the RTX series. IME all teflon/PTFE caps are very revealing, and maybe not what you are looking for. Polypropylene film and foil can be smooth and soft, not too expensive, and available. I have no experience with oil.

All of this IMO. YMMV.

 

Agree with Rodman99999 - you can try Takman carbon resistors.

Don't agree 100% with Eric and petg60.  All caps have coloration (every single one does) as opposed to using chokes instead of capacitors.  Agree with mickeyb - V-Cap oil caps are smooth but do allow detail to come through.

Jupiter Copper foil not our cup of tea but are slow and musical.

 

Not a fan of Mundorf but have used them with good results but nothing special to our ears.

Power supply I believe we used Motorola or Mitsubishi or maybe we used Mundorf I forget PS caps with musical results when we could not fit Nichicon PS caps - I am talking about the large capacitors not the ones placed on a circuit board.

Lots of responses and you have to try them out for yourself to see how they sound in your system.