21/0/9 or 21/9/0 on apc

21/0/9. Mana regen like that + bitchscuits and the summoner spell CDR are too good to pass up.

Unless you're a manaless AP. Then 21/9/0.

It really depends.

21/0/9 is more suitable for champs that has very little mobility & highly depends on his summoner spells for escapes, such as

21/9/0 is more of an AP fighter type of champs, where such mage champs can take in a few hits without bother, technically speaking, more defensive, such as

fighter-ish mids should take 21/9/0, while long range or poke ap champs should take 21/0/9.

i always do 25-0-5

so i guess neither. closest is 21-0-9 though

I think it actually is based entirely on the player and playstyle. I personally like to go 21/9/0 because the extra bit of defense always goes a long way for me, whereas I can usually manage my mana until I get Morellonomicon.

For me, I have simply had better success with 21/9/0 since I used it starting Season 3. I've tried using 21/0/9 and simply can't win with it without being carried.

That said, I play mostly Viktor, where I have to be in medium to close proximity most of the laning phase. Whenever I play Vel'Koz or Xerath, I do find the defense to a waste because I'm at a good distance away from my opponent most of the laning phase. During teamfights, I'm usually further back and playing keep-away from the other team. That said, if I'm playing against Talon or someone that instagap-closes, then I will probably go 21/9/0 just to prevent potential early deaths.

It depends on what you value more.

If you find yourself dying, just barely losing trades, then you might want to go 21/9/0; if you find yourself running out of mana or wishing you had your summoner spells slightly more often, go 21/0/9.

It's a similar question to taking AP or MR blues - one gives you more offensive power, the other helps you not die.

Personally, I'd say go 21/0/9 unless you need the extra defence.

Also remember that those aren't the only two options. You can go 9/21/0 if you need to be really tanky, or less common combinations with deeper utility for spell vamp, etc. - try to pick whichever masteries you think will help your champion the most.

Depends on the champion, really.