What speakers work with low wattage class A amps

Altec-Lansing 604-8G drivers in a 620 9cf cabinet. Classic that will sound good with 25 watts or less.

Reference3A DeCapoI.  No crossover electronics that waste power.  Just a high pass cap for the tweeter,  The Midwoofer is allowed to roll off naturally.

Relatively large cabinet for a stand speaker.  And the midwoofer also is relatively large.  Both characteristics combined yield excellent bass.

I drive my DeCapos with either a 25wpc OTL tube amp or a 35wpc Musical Fidelity Class A.

Sound magnificent, most musical I have ever heard except for ProAcs.  But the ProAcs need a lot of power and the DeCapos do not.

Speaker sensitivity 89 db and higher 

Zu, Tannoy, JBL, Klipsch, Fyne..something with +90dB sensitivity

Not all models by the above brands may be high sensitivity but I believe that they all of them do produce some models that are. The all new Martin Logan "Motion" series are all +90dB and they appear to be significantly improved.

25 Watts “or less”

The lower the amp wattage, the more limiting choices of speakers.  There’s a big difference between what speakers will drive 25amps vs a flea watt amp such as 4watts.  I have a 300B 8watt amp which necessitates that I have a very sensitive  speaker - 100db Volti Rivals.

Do you care if the speakers are bookshelf of floorstanders?  Floorstanders generally yield much better bass.

Do you care if your speakers are neutral- it’s much harder to find in very high sensitivity speakers?  I do because I plan to swap out components and want as neutral a system as possible to evaluate the components so I chose Volt Rivals.  I’ve heard the lower model Volti Razz twice and it sounded fantastic.  Klipsch, while very musical, seemed significantly less neutral.

Speaker sonic preferences are subjective.  It’s always best to demo them yourself.

A budget for your amps and speakers would be very helpful in narrowing your choices.  I’m assuming you have the preamp and cables budgeted if needed.

Generally speaking, tube amps have a pleasing magical midrange (some may call it coloration), less extension on the frequency extremes (bass and treble) and are less dynamic than SS amps.  However, there are s a few SS amps that have this pleasing midrange designed seemingly designed to compete with tube amps such as First Watt, Krell, GaN-FET type amps like from AGD, Atma-Sphere, Peachtree.