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

My homebrew Pass F5 is more robustly built than that Sudgen, and so is the XA-25 by a country mile. There’s a ton of stuff that just screams "CHEAP!!!!" to me. A 300VA toroidal is the bare-bones minimum for a 30 watt class A amp. A 400VA center tapped with dual rectifiers would have cost marginally more. What’s more, the power supply filtering is built into the amp boards. They’ve bolted everything to the bottom cover of the chassis rather than install a proper bottom plate. The chassis itself isn’t anything particularly remarkable either. Bottom line: it’s built to a tight budget. That’s an MSRP $1500 amp at best.

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. 

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.