For starters, I think you need to look hard at your requirements and expectation from an individual perspective, some futures you should be looking for are universal and some are specially focused on certain types of shooting.
For me, as a professional shooter one of my requirements is that the platform be night vision capable. This mean I'm looking for a chassis that can mount UNS, lights, lasers, the works. Sounds simple but I need to find a chassis that has the reastate to mount all that stuff in the right spots and not interfear when shooting of barricades and is bearable to carry about. On top of being able to mount the things I want, in the right place, I need a chassis that offers no/to minimal shift of those laser when loading, typically not more that a MOA of shift. Again this is just a exapmle of my individual requirements, but you get the idea. Hunters, PRS shooters, Palma guys are all going to have different takes on what you need from a chassis. In reagrds to tubes vs. open tops I prefer the tubes as they typically offer more mounting room but also because it feels a lot like a carbine forend and as a fight rifle, I think it makes a little more sense.
More on the side of the universal needs, as others have hit on already, you should really focus on adjustably. This is a huge part of shooting to your full potential. If your uncommortable and forcing your body to fit the gun as opposed to having a gun fit you you then you wasting energy that could be put to use focusing on the fundamentals or reading wind. I grew up cutting my teeth on a H&S Precision (LOP adjustment only) and sure you can make it work but after transitioning to an AI 2.0 it was a huge relief. Progressively I've moved on to the KRG, RACS and eventual to the AX which you can make fit like a glove and is all but effortless to shot.
Lastly magazine compatibility might be of consideration but doesn't need much explanation.
