You will not get "better sound" with one amp kit vs. another.
Main thing is quality of the wire.The $8 power acoustik/legacy/pyramid/the like kits that claim 8 gauge have power wire no better than a nice quality 12 gauge wire.
As was mentioned, the main difference is the quality of the wire. The cheapo kits may have much smaller actual copper in the wire than a more reputable brand.
The ebay kits with the over inflated ship rates are the ones to watch for. $9.99 for a kit + $20 shipping, what a deal there. Most of those are the good ole "3000 Watt" 4 gauge kits with 80A fuses...//content.invisioncic.com/y282845/emoticons/rolleyes.gif.c1fef805e9d1464d377451cd5bc18bfb.gif
you'll get some unreliable sound if you don't have good solid connections with any wiring kit, cheaper ones tend to have their connectors corrode and insulation peel off