Hey David - just my $0.02 as a person who still shoots IDPA and USPSA regularly, and likes them both. My short answer to your question is: shoot both. Any time I'm pulling the trigger, I'm smiling!
As others have said, these games are very different. IDPA emphasizes more tactical-ish aspects of pistol shooting while USPSA is more about movement and strategy. If you go into each game knowing that they are different, you will have a great time with either.
I think IDPA is better for beginners because you don't have to think about "how" you will shoot a stage. Typically, there is only 1 way to shoot a stage, and the game is to see which shooter can execute the stage procedure in the quickest and most efficient manner. Scoring is also easier to understand.
In USPSA, the things that I think make it fun, i.e. more rounds down range, less 'tactical' rules, no target engagement procedures, etc, may make the game a little more daunting for a beginner. It is definitely a faster game. There are also less rules around how you shoot a stage. Scoring is also a little bit more complicated though.
After awhile, you'll gravitate towards one or the other. I, like many on this forum, prefer USPSA (I got bitten by the open gun bug), but IDPA is also fun.
In a couple of months, I expect to see you posting about your first 3-gun experience... Now THAT's fun!!