So with 250 champ points how many would you put in reduce cost?Cost reduction trumps regen hands down in any situation where you are spamming spells.
So thats basically all DPS & Healer builds.
For tanks Regen comes into play more as they are spending a bit more time where they aren't constantly casting and the regen then comes into play more.
Also worth pointing out that @Dracane made a very good point there..... if your regen is fairly low to start with then the champion point passive is only increasing it by a percentage rather than a fixed value. SO a low percentage of a low starting figure is.... low.