So im trying to figure out what is better, flat mana runes or the ones that add up per lvl?

Per level equal the static runes at level 5. So levels 1-4 static is better, 5 they are the same 6-18 per level are better.

Considering how quickly you hit 5, I prefer per levels.

Considering your asking mana runes I'm assuming your talking about Ryze. Per level easily wins out in the long run. Flat mana runes just lose value so quickly in the game. Mana runes just don't provide enough umph like crit chance runes to make them worth getting the raw values instead.