I'm definitely a custom guy. My current rifle is pretty much perfect, but it took many iterations and thousands of dollars to get it to this point.
AI's are undoubtedly great rifles. I have lots of friends that have them, they are excellent systems. You know they are going to work out of the box, and well. Personally, there's some things I don't like about the AI system. I'm not a fan of the trigger, the ergonomics, or some aspects of the chassis' designs. However, that's strictly personal preference.
A custom can be made to exactly fit you, and for whatever your preferences are. If you don't know what your preferences are, you may go through multiple rifles or iterations of a rifle (time and $) to figure out what those are. Some parts may not play well together, and you and your rifle may become a victim of stacking of tolerances. Paying for a good competent gunsmith and quality components pays dividends, put still doesn't guarantee that it will take some further effort and frustration to get it to work 100%. But when it does work and fit exactly the way you want, it's like a well made tailored suit. But it may require going back to the "tailor" a few times for alterations to make it perfect, takes a few fitting sessions to get it dialed in.
An AI is the easy button. Take it out of the box, slap a scope on it, and it's going to shoot and shoot well. It's that really high end made to measure suit hanging out on the rack - might fit you, might not. It might be everything you dream of in a rifle, and after this point you may forget how to spell the word custom. Lots of folks on here very happy with AI rifles, and rightfully so.
If you know exactly what you want in a rifle, and have a good gunsmith, a custom is my personal preference and recommendation. If you are still figuring things out, it's really really hard to beat an AI.
Good luck in your decision.