I race any Indiana HS I can possibly make. The politics of the whole AMA/District 15 thing are disappointing as I really liked having the races liked together as a whole. Anyway, IndyRider is correct and about all you can do is go to their respective websites. All the series have their pros and cons based on whatever your agenda is. The different series tend to have slightly different track set up styles and crowds that just kind of click for different riders. i.e. I love GNCC's so I gravitate toward those type of layouts which is probably IXCR. You'll probably want to attend a few of each to see how it works. Typically I think the MAXC series is typically the most competitive and well run (except for starting on time). The one thing about the MAXC series I really appreciate is that when riders make comments or suggestions for improvement they don't fall on deaf ears and if there is some validity than many times you see changes. Track layout has been one of those for the better. I also have come to really like the IXCR series, the single most reason is that if you register online prior to the race at race day your sign up time is likely less than 5 minutes.
Many times the bottom line for me is simply location. IXCR has run several in SE IN almost to Cinci which for me is a little far to travel for a local race. One final thing to look at is most of the clubs have been doing a great job of securing new land for races which is great! Nothing like virgin trail. But be warned, if it is a mudder most of these new facilities parking areas will be a disaster and the virgin trails when wet can be a handful. That's why places like Stoney even when very wet can be rideable because they know how to work around it and the trail is so ridden in it's usually not bottomless.
Stoney is the stand alone series that is a trick bag for me. It doesn't suit my riding style and I hate the fact that I don't believe I've ever raced there and not gotten off course somehow due to so many trails. But Stoney is the only series IMO that really knows how to put on a race. They sound check, they always start on time, and they always get
results up right away. It's not my favorite place to race but it can be good and I think their youth races are very good.
Keep on working it and you'll find a mix of races that works for you. So unless you're a points hound just pick and choose and be thankful that Indiana seems to have a lot going on in HS.