They're both good.

Xbox Series X

Positives - Xbox is available. I can walk into a store and buy a Series X. That's definitely a positive. Another is Game Pass. It's one of the best deals in gaming but is $180 per year (but more expensive than PC Game Pass). This includes a lot of Day One releases which could otherwise cost $60 alone. Very good deal. Backwards compatible with older discs. Although I believe the library of older discs it accepts is limited, it's still a positive.

Negatives - 2 years in and it doesn't have any next gen games. AFAIK, all Series X games can be played on XBOXone. Extended memory is proprietary and expensive. There are also no exclusives. Almost every game available on Xbox is also available on PC. Eventually, the Activision/Bethesda games will be console exclusive but will also have PC releases. If you have a gaming PC, there are very few reasons to have an Xbox.

Xbox Series S

Positives - in addition to Series X Positives, the Series S costs $200 less.

Negatives - in addition to Series X Negatives, the Series S is less capable and has less memory. It's a great machine for its price but, as soon as you extend the memory, you're close to the Series X price point. The lack of a disc drive will cost more over time, too. Digital games stay at full price until the occasional sale. Those sales are usually still more than a used disc. Being able to find $60 games for $10 (or even free via borrowing or under $10 from thrift stores, yard sales, whatever) can make up the $200 difference of not having a drive pretty quickly. Controllers are good but come with disposal batteries. Feels cheap and is an additional expense to buy your own rechargeables.

PS5 (Disc Version)

Positives - it already has next gen exclusive games; good ones that won multiple awards last year. In addition, you have the Sony exclusives that compete for (and often win) GOTY awards every year. Some of these exclusives, but not all, are slowly being released on PC 1 to 3 years after release. The new PS Plus pricing is really good. The base price point is $60 a year and gives you PS Plus collection and 3 to 5 free games a month. The PS Plus Extra price point adds about 400+ games (about the same as Game Pass) for $100 a year. And for $120 you get everything above Plus another 300+ older games. PS Plus does not include the Day One releases of Game Pass. It is a great deal for the price and even more so for people who are new to Sony because almost all of the exclusives from previous years are included. Internal memory is not proprietary and is a lot cheaper than Xbox. An SSD can be used as an extended drive to store and run PS4 games without reducing load speeds and internal storage reserved for PS5 games. Haptic feedback on the controllers is game changing on first party titles.

Negatives - you can't find one and it is still not readily available in stores. You will not have access to some xbox games like Halo or Forza. They may be losing access to future Bethesda games and some Activision games. Though, depending on which games you are interested in, you may have time to save up for a PC to play them. Controller battery runs out of juice after about 6 - 9 hours.

PS5 (discless)

Don't buy this. It's $100 less than disc version. If you buy 2 or 3 $60 -$70 digitally games when you could have bought $10 or less used discs then you're actually losing money instead of saving $100.