Should I get Scaling AP or Solid AP Quientences?

I always get flat runes. They help with the early game, which is really the most important part. If you do well early, you do well for the whole game.

flat ap quints is what i use

spell vamp

Usually people go for flat AD and AP for early game impact. A few extra AP later on is rarely the difference in a team fight, but it can be huge in early trades.

Flat AP for the early trades for sure.

I break the patternand run scaling - but then, I also main Morgana and Viktor midlane.

You should run flat ap quints because they give you a pretty decent amount of ap early on. In general, runes are supposed to give you some edge in laning phase. Some players will run scaling runes for 2 specific reasons:

1. They expect the game to extend mid-late game. (Generally speaking, scaling runes will outscale their flat rune counterparts around lvl 6-9)
2. The stat that they're using the scaling runes for isn't going to be useful in lane. (Ex: you're playing an AD top lane vs an AD bruiser so you run scaling magic resist because it won't be useful in lane)

The way I look at all runes with the exception of scaling MR (which I almost always take 9 of in my glyphs), you want your runes to give you an early game advantage, so that you can gain an advantage and scale into late game harder through more exp/gold. Flat runes are almost always better than scaling.