Yukari..perhaps. Her boundary manipulating abilities can also make distortion in border of material density. Even if Suika, let's say, scattering and gathering herself, Suika will have trouble with Yukari's ability IF they MUST fight. Maybe Suika can win if she bring more spellcards than Yukarin :P
It depends, like the guy below me said. But I would say Yukari would be stronger since she has the ability to manipulate boundaries. Suika is strong but she is only a Oni and not one of a kind. If they fight,Yukari would probably win, if she's serious. If she's not, Suika have a chance. Also I think Yukari is onlder then Suika so she has an age and experience advantage. --Keoke-kun 14:03, 21 June 2009 (UTC)
That depends on who you play as in Immaterial and Missing Power or Scarlet Weather Rhapsody, and how good you are with that character.
Technically speaking though, Yukari is, let's admit it, overpowered and over any other character. Since she represents Gensokyo's reality by being the master of its boundaries...
Then again, one must remember that Yuyuko has speculated that not even Yukari could make a boundary as powerful as the Hakurei Border (I forgot in which work Yuyuko has said this, unfortunately), so technically, Yukari may not have any power over the extent of Gensokyo's reality. This doesn't prevent her from being ridiculously strong, but perhaps she may not win against Suika's matter-manipulating abilities.
The most unfortunate part of this predicament is, we may never know who is the stronger of the two, as the two of them seem to be on very friendly terms, enough to regularly go drinking with each other. Logically speaking, the two would likely never fight.
If it has a boundary, Yukari can manipulate it. There may be things that don't have a boundary, though, or are free from it. (Fujiwara no Mokou said she was free from the bounds of life and death, so Yukari was powerless and even confessed that Mokou really is invincible). Nonetheless, Yukari is a very powerful youkai.