[Xiaomi Mi 11 Ultra] roirraW "edor" ehT:
There's a long list if I break it down completely, but this is the best I can do off the top of my head:

Samsung uses hardly any screen real estate to display what quick-setting tiles you have to choose from (to drag and drop among the normally displayed tiles, and choose their order). Makes it much more time-consuming and just a general PITA to customize. I think they've improved it slightly but it's still not as optimal as it was on pure Android a la Pixel.

Although it's nice that the screen can get so much brighter than the Pixel's did, it's also true that it can't (easily) be made to be as dim as you could on the Pixel - like at night when you don't want to blow your night vision out. I've gotten used to it but I still prefer being able to go dimmer when I want.

This is true of any OEM skin like Samsung's which isn't close enough to stock Android: you can't use Samsung's widgets if you're using a third-party launcher (like Nova Launcher Prime).

For so many capabilities built into the phone, there are effectively two choices - Samsung's and Google's. I ended up with duplicate contacts when I transferred things over from the Pixel due to Samsung's less than optimal experience, versus on the Pixel just restoring everything that's capable of being restored from Google's cloud backups.

I don't like my status bar clock on the left. I do prefer to have seconds showing on my clock.

I would be able to comfortably fit at least 8 quick-setting icons across the top when you pull it down halfway. I'd like to be able to have that choice (again, easily).

I confirmed that my brother with his S9+ and my co-worker with a Note 8 or 9 had the same experience as me: GMail and Hangouts/Chats/etc notifications are hit and miss. Sometimes I don't get a GMail notification on the phone until an hour after I've already seen and read the very same email on the computer. Sometimes I get prompt notifications for chats and sometimes I don't. Most of the time, I don't get notifications when I should. My brother thought that's just the way Android is since the S9+ was his first. I never had that experience on the Pixel 1, HTC 10, and I don't think on my LG G3, or even my Galaxy S3 before that. I loved my S3, but that was a very long time ago and things have come a long way - and before I tried stock Android (other than custom ROMs, which don't really count).

There's more, but in summary, on the Pixel, everything just worked. On the Samsung, it's very frustrating.

To each their own, and the hardware on my Samsung is awesome, but it's the software I don't like. Before I had the Pixel, I was skeptical that I would like stock Android as much as I did. The main reason I never got another Pixel is because the first couple of years, I was waiting for a PIxel that would have 256 GB of storage, which never happened. I was happy to get the Samsung with 512 GB of storage, and I have a 400 GB Micro SD card with my music, which I prefer in FLAC format. The Pixels don't have MicroSD slots, which is a bummer, but at least the Pixel 6 Pro has a model that has 512 GB of storage. I'm not entirely sure I'll get one, but I'd say I'm 80% sure. If I don't, I'll just be holding out for one of the next Pixels that come out. Personally, at this point, I would be a lot more satisfied if they had 1 TB model, but it does suck I wouldn't just be able to plug my MicroSD card in whatever phone I get if I get one with a MicroSD slot.