What Class A is better? SUGDEN FPA-4 or PASS LABS XA-25

In all reality, they're two completely different topologies. Pass doesn't sell any single ended class A amps anymore. They're all push-pull which is why the XA-25 is a more muscular amp. That Sudgen is clearly a single ended amp. 

Hello jperry,
My speakers are Monitor Audio PL-300.
They sound very detailed and have fantastic soundstage.
Thanks once more.

kosst_amojan
I have no doubt that PASS LAB has fantastic amplifiers.
I understand your opinion, and thanks about it.
My intention was to know the preference of the audiophiles who have listened Sugden and Pass.

As someone mentioned, it's warmer sounding, which is generally expected of a single ended topology. That's not a very common solid state topology. Most turn to tubes for it. It's characterized by a dominant second order distortion harmonic. If that's the sound you're looking for, the Pass Aleph amps or some of the First Watt amps might interest you.