I bought three 10” 4-ohm speakers during a sale to try in the Vibro Champ, an amp I record and rehearse with regularly. The M-10C was the winner for retaining volume, clean headroom and best breakup. The other two speakers were Alnico magnets. They all sounded great but the 15W Alnico seemed inefficient. It was noticeably not as loud The 25W paper Alnico was a little too creamy when it was overdriven. It would probably sound better with an EL84 type amp. The Ceramic M-10C is staying in the Vibro Champ as the best if the Fender style shootout - but you do have to lose the tube cage as the magnet on the M-10C is ginormous in comparison to the stick Celestion. That’s probably why it sounds so good!

This speaker brought new life to my Princeton Reverb - it’s balanced and sweet. A huge upgrade over the stock Jensen!

I wanted a vintage C10N for my PR, and this seemed to be the closest modern replica with paper former. Haven't turned it up to gig levels yet, but it sounds good at home. Fast processing and shipping. Jupiter claims they broke in the speaker, which I paid extra for, but how can you tell other than the fact that the speaker sounds good? Beautiful blue frame.

I had a hand wired clone of a blackface Princeton built a few years back and have gone thru quite a number of alnico speakers trying to capture the magic of the circuit with little success. I probably should have tried a ceramic sooner, but I really like alnico speakers in another vintage clone I have (brownface) and thought they would bring the same magic to the Princeton. They didn't, and I'd actually thought of selling the amp because it just seemed so uninspiring when plugged straight in.
I decided to finally try a ceramic speaker in the amp and mulled over typical options, but this 10" 25 watt paper voice coil speaker really caught my attention and I'm so glad I decided to go with it.
It's a super balanced speaker in the amp, without booming bass or strident highs. It's not muffled, nor does it project any unpleasant frequencies.
What it does do is just sound fantastically balanced, and to me, gives off some type of magic or mojo that turns the amp into a real keeper, whether using pedals or not.
Purchasing speakers to try in an amp can be hit and miss, so I hope my experience can help someone else know what might work in their amp and what to expect. Good Hunting!