avalanche would be cheaper and possibly louder due to more surface area but the XXX will sound better so it all depends on how much money you have and if your looking more for spl or sq
YOu sound like you got the same question that i do except that you actually have money..i was looking for mainly spl and someone in another post told me that a 15' or 18" SX would be just as loud as the XXX but about 100 bucks less so i was thinking about getting that and maybe you should too if your looking for loudness