I know it's common to use a 120cm sling with overhand knots for personal anchor, but for some reason I haven't seen it suggested to put a carabiner through one of the knots. I find this simplifies the following aspects:
(1) Attaching to the harness while climbing
(2) Shortening the anchor attachment
(3) Untying the knot after it's been loaded
With well tuned knot placement, I feel this matches the convenience of PAS (which I do find more convenient than just a sling with knots).
(I use a non-locking biner because an overhand knot in this configuration probably isn't secure, so I'd never rely on that middle carabiner by itself)