There are thirteen Standing Stones scattered across Skyrim, and the game lets you swap your blessing for free any time you walk past one. That generosity is exactly why most people never think hard about the choice. You grab whatever's near the road out of Helgen and forget it exists. So I sat down and ranked all thirteen by what they actually do over a real playthrough, not what the loading-screen flavour text promises. Tiers, roughly best to worst.
The ones that change how you play
The Lover. This is the sleeper everyone sleeps on. The Lover Stone gives a flat 15% boost to every skill's experience gain. Not combat skills, not magic skills. All of them, all at once. On a fresh character that's the difference between hitting Smithing 100 in an afternoon and grinding for a week. It's not flashy in a fight, which is why people skip it, but if you're building a character from scratch it earns its keep faster than anything else here. I park new saves on the Lover until the build's mostly cooked.
The Steed. Carry weight +100 and, the part nobody reads, your equipped armor stops counting toward weight and stops slowing your movement. That second clause is huge for heavy-armor builds. You wear full Daedric and run like you're in your underwear. For an unenchanted melee character who's drowning in loot every dungeon, the Steed quietly fixes the single most annoying thing about the early game. Genuinely top-tier and almost nobody talks about it.
The Atronach. 50% spell absorption, +50 max magreserves, but a brutal 50% slower magicka regen. This is the famous tradeoff. Spell absorption is fantastic against mages and dragon breath, and stacked with the Atronach perk and Alteration you can push absorption near the cap and become effectively immune to magic. The catch is real though. That regen penalty wrecks any caster who relies on regen instead of potions. So it's S-tier for a hybrid who restores magicka another way, and a trap for a pure mage who hasn't planned around it.
Solid, situational, or just fine
The Lord (+50 armor, 25% magic resist) is the workhorse defensive pick. Boring, always useful, the one I default to on survival runs. The Atronach's cousin in spirit, the Apprentice, doubles magicka regen but doubles magic damage taken, which on Master difficulty gets you exploded; fun for a glass-cannon meme, dangerous otherwise.
The combat-skill stones, Warrior, Mage, Thief. Each speed leveling for their six associated skills by 20%. Strictly weaker than the Lover for general use, but if you know exactly what you're building they're slightly faster for that lane. The Tower (unlock Adept-level locks once a day) is convenient and utterly skippable once you've got a few lockpicks and the Novice/Apprentice perks.
The Shadow (invisibility once a day for 60 seconds) is a nice panic button for a stealth character or a quick getaway, but a single Muffle/Invisibility potion does the same on demand. The Ritual (raise nearby corpses to fight for you, once a day) is pure chaos comedy near a battlefield and dead weight everywhere else.
The bottom
The Serpent lets you ranged-paralyze a target for a few seconds, once a day, with a little poison. It's not nothing, a free paralyze on a tough enemy can save a fight, but once-a-day utility ages out fast as your gear improves. And the Lady (+25% Health and Stamina regen) is the runt. Regen is so slow in combat that the boost barely registers, and out of combat you don't need it. Last place, no contest.
If I had to crown one, it's the Steed for any non-mage who hates the inventory shuffle, with the Lover stealing it for the leveling phase. For mages, Atronach if you've built around it, Lord if you haven't.
So. Which stone do you genuinely never swap off, even when a better one's right there on the road?