A higher Qtc alignment will generally give you higher overall SPL, will be more peaky, and have less transient response/greater group delay. All things that if over-used, will sound like ***.
On the other hand, a lower Qtc alignment (lower than .7 or so) will result in better SQ at the loss of output. A lower Qtc box will generally be larger in size and require less power to reach Xmax.