Captured line is the best morale line ever. It's good runner that gives morale penalties, while captured gives morale boosts (at the cost of stars, but that's fairly easy to regain). Now, since the general can only be captured after routing (once, if rallying and routing again, this becomes more complicated), it's very hard to get in battle and easier to get by retreating through sea ways, but it's very strong.

Natural leader is extremely hard to actively get or boost and the rest of the morale lines are random.

On average I agree on not paying for ransom. It's mainly useful if you still need to pay while retreating by sea or if there's some good units in there. I still usually do it but that's mostly as a tribute for service well done, unless they did do poorly. Then it's execution time.