Probably the most commonly recommended low-markup prebuilt brand these days is
Skytech. It has held up to scrutiny from reviewers (like Gamers Nexus) with decent build quality. They don't commit fraud with components like some of the other popular budget brands you'll see on Amazon have been caught doing many, many times (ex. STGAubron).
Skytech's bigget competitors are probably
CyberpowerPC,
iBuyPower, and
CLX Gaming which are also known for custom prebuilts where the buyer picks all the components, but I suspect most of the PCs they move are regular prebuilts. You might find some negative feedback, I'm sure, they're not perfect, nobody is, but all three are solid brands.
The
HP OMEN series is well-reviewed, and well built. Probably the best option from the major companies. Avoid Dell's Alienware in particular. They're just determined to not sort out their weaknesses. Probably also worth mentioning is the
MSI Codex R2. MSI has been making a greater effort to make itself relevant to builders than other companies in recent years. Meanwhile, this particular prebuilt model has been getting the top recommendation for the best value among prebuilts from some of the top publications, currently.
Origin is a boutique builder with a higher markup that has done well in the secret shopper investigations in the past. One other boutique possibly worth mentioning is Asmongold's upstart brand,
Starforge. The first gen took a lot of heat, but the second gen got strong reviews from the most critical including Steve at GamersNexus.
Microcenter's in-house brand
PowerSpec is worth a mention if it's an option to you. They're sort of the Kirkland of the computer world: an ACME kind of brand you can trust.