Was typing this while Rock posted, conveying much the same idea.
The ideal recording position is the best sounding spot you can successfully manage to record from without stressing out.
Assess and adapt. The specific answer varies with each situation. Depends on the fest. Sometimes you can get a good idea of the best spot in advance- from what you see when first walking in, from listening to the background music through the PA before the show starts, from having been at that venue for similar past shows, from checking photos of the venue beforehand, from asking other tapers. Given the two specific choices you mention with no other info, I'd setup next to Grawk.. unless there's a potential problem with recording from there that makes stack taping off to the side the better option, such as a super-unruly crowd, crazy moshing going down there, or any number of other things.
The fundamental constraint is being able to successfully record. Getting the best sound is dependent on that. But focusing on the sound alone, my 1st acoustic preference is to be centered and positioned at the forward-most edge of the 'sweet spot'. The sweet spot being wherever the sound is clearest and most involving, with good balance. That's frequently 20-30' back in the center, but it might be a further, it might be right up at the stage-lip/rail, or it might be off to one side in line with one PA stack if the sound there is clearer from a position closer to the stage than it is from an centered sweet spot that is too distant. Also, there may be more than one sweet spot. Sometimes the forward edge of the typical centered sweetspot is some distance back, and the sound gets muffled and less-clear forward of that.. until you get right up to the stage-lip or rail where fill speakers and the direct on-stage sources create another sweet spot.. which might be way better still.. or not.
If you get the chance during the performance, move around and listen with a critical ear to assess the situation at various positions. Mentally take note of the good potential recording spots, even if you're unable to act on that at present. Doing that will better prepare you for future recording, even if its at an entirety different venue.
Your preference for the sound you like may differ from other tapers. Maybe you crave a very dynamic and super lively up-front sound, or maybe you prefer a more evenly mixed but less dynamic sound from a bit further back where things gel more.
I'm now older, and the open rig I currently run is somewhat larger, but I used to run a rig I specifically designed for use right up front/center in the crazy heart of things, where the sound is most rich and impactful and the most enthusiastic audience packs in. This was back when most open rigs were bigger, heavier and bulkier. The rig was small and light enough that I could just grab the stand with small recording bag attached to it and bug out of there if necessary, or easily pick it up and shift over, forward or back while recording as necessary.