I have bought both assembled, and kits to build it yourself, as well as completely individual parts.
In my case individual parts and kit form work out best price wise.
The only thing you really have to make sure to think about is the availability of stripped uppers right now.
I just ordered a socom barrel kit for another build specifically due to the fact that I can not find a decent priced stripped upper in stock. Seems most of the companies are keeping them to assemble uppers or to put together kits.
Even PSA is selling assembled uppers, but none stripped in stock atm.
If it comes down to an assembled upper with just the handguard being what you dislike, that itself isn’t a deal breaker.
Now, if the barrel and handguard and… Then it becomes too much of an extra cost to make it as you want.
Most of the reasonably priced assembled uppers I have seen lately are stock handguards with front sight gas block. For the same price I found kit-form with a free float keymod handguard. It may not be the exact handguard I want, but at least that keymod handguard looks better in the parts box than mil-spec parts that I will likely never use.