It depends. Amplifiers built to be both stable and deliver max power at .5 ohms are usually a totally different animal than one that will give you maximum power at 8 ohms.
First you have the high current versus high voltage argument and my opinion of high voltage 12 volt amplifiers may be a bit biased because I never ran one that worked out for me on a subwoofer with modern electronic music. Generally, an amp that gives you a boat load of power at 8 ohms will be high current and it is limited by the constraint of one's 12 volt electrical system trying to step up 12 volts DC to as much as 120 volts, or more, AC. Granted, there are some exceptions to this, but those are few and far between while being extremely HUGE (think US Amps surfboard here!). Just don't believe the hype when a certain nuthugger claims their bonerriffic old school amp can produce 1,500 watts RMS all day long on a 60 amp slow blow fuse at 8 ohms because it is high voltage. DEMAND a 30 second burp at max power while measuring the actual output power if anyone ever tells you this, and report back as to what happened.
Next, a low impedance amplifier capable of delivering max continuous power at .5 to 1 ohm will generally be of the high current variant. The old school of thought was that it was easier to make power by running an amplifier close to a theoretical short, but it was harder on the internal components within the amplifier. As long as you can feed it the supply current it needs, you should be golden for output. Now how long it will last is a toss up. My old Crossfire BMF1000d had a new board put in it in 2004, and has been going strong running at 1 ohm since then. It is currently rocking along in a friend's car! I still have several old school Orion HCCA 225s because I can't let go of the past, and let's just say I can come close to frying hot dogs on the heat sinks if I run them at 1 ohm.
Finally, you must define SQ when it comes to a subwoofer. Technically a "Sound Quality" sub setup would be one that properly blends with the rest of the system. As long as one is running an adequately designed amplifier for their given impedance with a properly implemented sub, the final impedance load shouldn't impact sound quality as much as one would think! After all, most subwoofers only reproduce a fraction of the audible musical spectrum and most individuals can't even hear distortion in the sub bass spectrum until it reaches double digit percentage levels (i.e. 10% or more).