there is no difference in sq, however almost any amp will put out more power when it sees a 4 ohm load and this can make a difference. more power usually sounds better.
The ohm load of a speaker is the amount of resistance the speaker shows to the amp... the higher the number.. the higher the resistance... Most car audio speakers come as 4 ohm speakers... this is the standard... any amp is capable of driving a speaker at level... Ohms work kinda like a hose... if you have a garden hose and a fire-man's hose... the fire'man's hose can provide more water.. because there is less resistance...
Be WARE... the lower the ohm load the more power will be drawn from your amp... check specifications on your amp... most amps are not stable in bridged mode bellow 4 ohms...