I dislike the .45 ACP mostly due to the experiences I have had with them. Initial usage was Marine Corps issue, which generally had worn barrel bushings and pretty well use over all. Accuracy was adequate for close quarter combat and use in tunnels, but sucked for range use, including qualifications. To qualify, several rounds had to be fired on target to see where a particular weapon would hit, you would post black stickers/pastees (not the kind I like) to compenate for the inherent inaccuracy.
With that kind of introduction, I have never trusted a .45 for accuracy since. I know there exist better .45s than military issue, but I just can't overcome my experiences with them and am unwilling to put down any money for something I expect not to like.
My intro to a 9mm was a Star when I was about 18. It was used, but functioned great and was fairly accurate. Round two with a 9mm was a Browning HP (privately purchased) I carried instead of the standard .38 issued to us air wingers. It was dead on accurate, provided terrific fire power and was better than anything the Corps had to offer as standard issue.