Best Tube Amp for High Sensitivity Speakers: 45, PX25, or 300B?

Depending too your budget and type of musicyulike and speakers

Before I do that, I would love to consider several things:

#1 independent wired to the listening room. You might already did it! A great step IMO. If you like to go further, make it two. One for analog, and one for digital.

#2 clean power. EMI/RF problems sometimes are real problems for some people.

#3 room treatment. We, I mean, I listen to the room sounds first, then the other things in the system.

#4 like @audioman58 said. I sometimes like listening some classical, big sound stage, huge dynamic, etc. 300b or those 2w/8w amp really can get them there? I tried the "two years waiting" amp, I like it very much. But, some music want more.

Try something different like the 211 tube ,or 845   More then enough power and sound very nice 

https://caryaudio.com/products/cad-805rs/

a dedicated line yes awg 10 if possible , and as I did 4 wire one a common ground 

the other ground a isolated ground in its separate path connected to its own grid to ground more monies but worth it you don’t need to isolate the digital after this .

buy a very good Ethernet switch , depending on your budget the   SW8  only $600

or top of the line  innuos $3700. Depending on your dac and quality of your audio system  what you can afford , the AC outlets buy quality Gold over Copper Furutech  or another name brand ,even Pangea $100 AC outlet very good . And on router for sure a 12v minimum 4 amp Linear Power Supply , any gsrbage wall warts need to go $5 junk noise makers , little green computer sells for $299 and never use stock power cords ,at minimum on the LPS power supply a Pangea Sig MK2  for example  I even put a synergistic purple fuse in the LPS as well as the upgraded Ethernet switch , each one  small but important  improvements ,

and Ethernet cables cannot be low end or your streaming will suffer, this too applies to the USB cable. Everything counts , I am still working on upgrades  last 

your dac , to me as the source how much can you spend $$. Myself semi retired have to save for more expensive items , the T+A 200 dac  I still have a few months to go to save , is imo and many others dacs we have compared it to directly in our multi state audio get together for its $7200 price a true bargain it beats anything under $15 k and more and has HQ player built into the platform to give you the ability to find tune this to your audio system ,to make it better still. 

I think the OP is mistakenly ascribing personality to the 45, 2A3 and 300B valves. What matters more is the circuit design and parts used. I have a 45 SET custom-built by Will Vincent (autospec) on an ST70 chassis that turned out beautiful! Plus a Japanese Sanei SA-560A 2A3 SET made with Tango iron. This I won at an eBay auction from a Japanese seller. It is the quality of the whole amplifier - the gestalt - that elevates the performance rather than the specific tube type!

I like low-powered tube amps of all designs--pushpull, SET and OTL--so I am not so wedded to a particular design.  As jasonbourne71 stated, it is the particular design and parts used that matter most.  In particular, the output transformers and interstate transformers (if used) that matter a lot.  

I do have some tube preferences (meaning I've heard a number of good amps made with a particular tube type), but it is not absolute such that I universally prefer something made with that type of tube over others. 

Of the three small triodes mentioned, I tend to most like the 45 as long as it is used with suitable speakers.  I own a parallel 2a3 amp that I used with 99 db/w efficient speakers and a 45 pushpull amp (both have sufficient power for my purposes, but then again, I don't play the system very loudly.  I currently run a pushpull 349 amp (5.5 watts per channel) that I like a lot.  I tend to prefer the 45, 2a3, 300b over the larger transmitting-tube SET amps (211, 845) although these can sound very good.  For pushpull amps, I also like a number of old and new designs that employ 6L6 and KT66 pentodes.  For really exotic tube types, I like the 350B, 349 (pentodes) and the 252 (triode somewhat like a 300b).

For the OP's 96-97 db/w speakers, it might be possible to use the three triodes mentioned (particularly the 300b), as long as the owner is willing to accept some restriction on very high volume listening.  I personally feel that some compromise in that area is worth it.  For a safer bet on compatibility, something in the 40 watt range should be sufficient.