Personally I stopped custom roms a while back. I’m not hardcore in the anti-google camp though.
If you are, obviously custom roms will be all you should be looking at. Tons of good recommendations in this thread already.
If you’re not in this camp though, the default pixel experience has been great for me and might be for you. I find it the least annoying of the oem experiences (not cluttered in features I’ll never use, simplified settings menu where I’ve never had to use the search on since it all made sense etc).
I’d say use the stock rom for a few weeks. If you hate it, custom roms are always there for you.
I’ve got the regular pixel 9 with 256. It’s not limited to 128, it just is the base model size.