I have been doing this for a quick minute and have found shooting is shooting. As others have stated, I have also found that generally speaking USPSA shooters are better shooters overall. There are exceptions but the way the game is played USPSA simply makes you a better shooter faster, IMO. I shoot both and have drifted to IDPA over the years simply for the ease of being able to shoot more big matches without burning a lot of PTO. It did hurt my USPSA game significantly. That's probably why I have been trying to get in more USPSA. lol
Ultimately both are great avenues to increase one's proficiency with a handgun. Be kind and welcome new shooters to either sport, it can only grow the community and spread the desire to maintain and fight for our 2A rights. IMO