Which caliber is the best when carrying a CCW? I am a newly licensed permit holder.?

Looking for some serious feed back please. I am currently carrying a 9mm (Beretta PX4 Storm), I just recently found out that they have make a 45 ACP (Beretta PX4 Storm) as well and am thinking of purchasing one.Does it really matter? To each his or her own on the type of pistol you prefer, I personally am a Beretta man myself. I just wanna know which caliber do you think is better or worse? Thank you!