I started using Penn level-wind reels because that's all I ever knew from when I started fishing as a kid. Then I got into it and needed another rod and reel and thought I should at least give the single action (aka knuckl-cruncher-masher-duster-buster) a try, and so I bought the Diawa M-one. It was lots of fun, far less work to keep up, and inexpensive too.
Then one day I hooked a huge salmon and lost it on my level wind because the drag was a bit too tight, and when the fish pulled (this after taking out about 100 feet of line) and I pulled, the line broke.
I thought to myself: Would this happen with the single-action Diawa? Answer: Probably not. The single wind reel allows for more "feel." If a fish wants more line, the line goes out. Sure, if a person grips the reel and refuses to let it move, the line (or the rod) can break, but that's not about to happen unless the person using the reel is clueless. When the fish pulls, the rod bends and it's obviously time to stop reeling and start palming. Simple. With a level wind, the correct amout of drag often remains a bit of a mystery: is there too much or not enough? It's hard to say sometimes, and it's certainly hard to "feel." With the singl action reel I actually "feel" as if I'm in control of the reel, which is a good thing because I know what I want and when I want it. But with the level wind the reel seems to be in control, which is only a good thing if the person holding it has no idea what to do.
Moral to the story? Now I use level winds for bottom fishing and single action reels when trolling for salmon. I've used both, and I must say that there's nothiing better than feeling the palm of my hand burn as a big fish peels out the line.
Remember, it's called "fishing," not "catching."