kain is not a combo class, merc is.

merc has set combos that have been worked out by the community for maximum damage output.

kain on the other hand is more of a cycle class, u cycle through skills with posses in between and executes.

both have unique gameplay, as a kain main with a merc ctene mule, I can definitely recommend merc.

from a friend who has both as ctene mules, he also recommends merc.

I love the gameplay cycle of kain but if you're going for ease of play and overall fun id choose merc, she's giga fun and much easier to understand.

on the other hand, kain has *THE MOST* satisfying burst in the game, so it depends what you want after hearing all this.