Like raw said it depends on the champion and what the other choice for talent is. As for seraphina, imo, for sure go crit wherever you can. Crit on her 4 power hits is very valuable. Ik using it 3 seconds faster sounds good too, but that just means you don't go out and attack again for 3 seconds, not a big deal. What ironforge said goes both ways, 5 or 2.5% cooldown reduction is nothing to get excited about. That's maybe a second off cooldown.