Lots of good info so far here. Good work gents.
One thing to consider in the HPDE vs Autox debate is cost. HPDE are usually much more expensive. Usual fees are about $150-250 per day for an HPDE, plus material costs (brake pads, rotors, fuel and tires). An AutoX can be about $40-60 for entry fee and material costs can be pretty much nil. HPDE's are much harder on a car compared to an autox. One thing I do prefer about an Autox over HPDE for a new driver is that its relatively low speed. The chance of doing severe damage to yourself and your car is much less in a low speed parking lot. (Granted you can do damage in both if you try hard enough
) However, big plus in an HPDE is seat time. you get much more seat time compared to an Autox. But you pay a lot more. I'd look into practice or test an tune days at your local SCCA chapter if you want more runs per day in an AutoX.
I'm glad I got my start in Autox. You learn very valuable skills that you can use on the road as well as later in a HPDE all in a low speed and safe environment. Of course, nothing says you can't to do both! However, I'd rather spin my car at 50 mph in a parking lot around some cones AutoX) rather than 100 mph into the grass and barriers (HPDE) with my brand new car and brand new license.
Good luck!