I use and swear by the synthetic leather lines!
Fritz's tracking line has been in nearly continuous use year round for about 5 years now, still looks brand new - sometimes requires a good cleaning of course.
Umsa's also has been subjected to serious abuse - and I use these lines with multiple dogs (girls get her hot pink, boys get his blaze orange), and in every cover (high, weedy, thorny cover, short grass, dirt, mud, rain, sleet, snow...). Most often a good portion of the line is dragging behind me in training, so again - lots of heavy use on the line. They hold well.
I have dogs that pull hard on tracks too.
I generally avoid balls in that I worry about choking/swallowing the ball...... but my dogs all love our jute balls. Only problem is that they wear out faster than a hard rubber ball on a string.
As for handles, Fritz once got a toggle handle stuck between his toes while running back to me with one of the hard balls on a string/toggle handle. - my heart stopped........... but he was OK. I think the toggle handles are better than the loop handles tho.