Best electrolytic capacitor


what are the best electrolytic capacitor for tube amps?
Mundorf, Nichicon kendeil or ? ...

The cut of the vent that is on the top of a AN Kaiser capacitor, tells me that it is very likely manufactured by Rubycon.

Each capacitor manufacturing company tends to use their own unique venting cut on the top of their given aluminum capacitor cases. That vent type and style on the top of the Kaiser Capacitors, says ’Rubycon’.

Importantly, for the purpose of clarity in the area of potentials in ambiguity... this does not mean it is a regular line item from Rubycon with only a change in the skin on the aluminum body. Custom work can mean custom design.
Yes, custom design! Nice sounding. 
How long is a piece of string?

What source, what resistors, what wire/pcb, what transformers, what topology, what tubes, what speakers?

Just did a full re-cap of my tube amp. 

What caps are you asking about?

The big power cans, or others?

I agree, Elna Silmic II. For the big caps, Jensen 4-pole if you can get them. Otherwise, Mundorf is fine. 
Are you recapping a vintage piece of gear? If the caps are 30-40 yrs old, they most likely need to be changed out with new caps. 
Never buy NOS electrolytics. 

I’d just check images of gut shots of high end tube components that you like and see what’s in them. You’ll likely find Nichicon, Elna Silmic, Panasonic, etc. 

I find that using a bypass film cap 1/100 the value of the electrolytic soldered to the + & - tabs or wires smooths out the high end of certain components too, but that’s not anything new. 

Elna Silmic II Are not available for high voltage tube power supplies.  Too bad. 
From the AN website:
"The Audio Note (UK) KAISEI range has been developed over the past years in collaboration with the engineering team at Rubycon (of Black Gate fame). Whilst working on our top of the line Black Gate replacements (which we should releasing toward end of the second half of 2016) we realised that it would be possible to put together a range of more affordable electrolytic capacitors that use all of the same materials as these supreme components (the same special electrolyte, foil and construction quality) apart from the hyper expensive and extremely difficult to produce Graphite impregnated paper, so the only difference between the KAISEI capacitors and the forthcoming Black Gate replacements is that the paper is not graphite impregnated in the KAISEI, otherwise they are the same."
I tried them in high capacitance values as coupling caps, bypassed by ClarityCap MR film caps, in Pass ACA 1.2 kit Class A monoblocks.  They sound fine after a long break-in cycle.
Mundorf Mlytic caps are very good for a lot less money than the AN electrolytics, but the ANs are the best sounding I have used. 
The Epcos Sikkorel is the best outside of the unobtainable BG's to me.