Both great, but VERY different.
Quality.... both excellent (I own a TH500 and gigged a Puma500 for a couple of years).
Size/weight.... Puma500 is stupid small, TH500 is stupid light!
Tone:
Puma500... TOTALLY clean, even, with a crystal clear upper treble and very even response. Very 'through a mixing board' sort of vibe. Closest other head to it is the Markbass F1/F500.
TH500.... bigger low end, a bit bloomy, some 'vintage' distortion always present in the mids, nice ability to increase distortion from mild growl to all out grind with the 'drive' control, more vintage up top. Closest other head to it IMO is the TC RH750, but the low end is much deeper/more open than the TC. Similar warm, wooly, midrange punch.
Both are A1 pieces of gear. PBass playing classic rock... TH500. Jazz/Fusion/Pop with a modern bass or J bass... Puma500 (oversimplification, but you hopefully 'get the drift').
Max volume of both seems similar.
In the US, the TH500, with one of the 10% off Musician's Friend discounts, is quite a bit less expensive than the Puma500 (around $400 less).