I decided to do a build first. I had originally decided to just do something inexpensive like a PSA parts kit special and a lower and just assembling the lower. But I figured I'd want to change things and want something more, so I decided to research, trying things out when possible, and do a build that is close to what I'd consider ideal, which was expensive, but I really like the result. I might do a couple of things a bit differently were I to do another build in the exact same vein, but there's nothing about this rifle that I actually dislike, just small areas where it can be made even better.
My second AR will be complete next week, and this one's also a build. I wanted to go cheaper and simpler, while still having some things I wanted that tend not to come standard in complete ARs on the market (if you can even find one these days, especially at a reasonable price), such as a lightweight barrel, no-FA carry handle upper, and a couple of retro-ish features other than the upper.
What I like about builds is I was able to get exactly what I wanted, or close enough in the latter case (the panic has made parts availability and pricing an issue, especially lightweight barrels and stripped receivers; in normal times I could have gotten it exactly as desired). After looking around I've noticed that I'd have a hard time finding a complete AR somewhere that would be the way I want it; something like my first build is basically unavailable, and something like the latter would be tough to find, if I could find it. I'd have to buy and replace a lot of components on a stock rifle to get what I want, including possibly having to replace the upper and/or barrel.
So, depending on the specs you want, you may have to build or rebuild to get what you desire. However, if what you want is available in stock form from someone, it is actually available for sale, the price is one you can afford and are willing to pay, and at most you might want or need to replace some small parts, and you wouldn't save any significant amount of money doing a build, then I'd say buying a complete rifle would be the best option. Builds were better for me, and it's possible I might only ever do builds and not buy a complete, stock AR; but they may be better for you, or buying a complete rifle may be better. Again, it comes down to what you want out of it.