If you do Parker just make sure you get some practice during the week, the weekends can be hazardous.
I'm going to recommend the lower river for a couple of reasons. If you launch below the diversion dam north of Blythe you'll have almost no problems with rocks getting stuck in the jet, no huge boats aiming to take you out, and if you launch after noon the water level won't be an issue. I launch at the public park/marina on the north side of I10 ($15), it has a little bay area so you're not dropping right into the current (good for practicing your launching/retrieving skills).
No matter where you go, just take plenty of time to idle around, run it up and slow down several times to get a feel for it.
And most important... WHEN IN DOUBT, THROTTLE OUT!!!