You'll find a lot of opinion in the answers to that question, not too sure if there is a lot of fact or case studies to support a valid answer. A lot depends on the wheel base of the tow vehicle. Mirrors play a big part here too. If you can see down both sides of the trailer clear to the rear marker lights, then your mirrors are pretty good.
Personally, I find towing a medium length (25-28 footer) is the easiest to pull if your wheelbase is long. I have not pulled anything longer than that.
A short trailer is more difficult to back up, it easily gets ahead of your anticipated turn
A long trailer is easier to back up, but takes more real estate to push it around
A short trailer is more prone to sway caused by improper loading (front or rear heavy)
A long trailer is more prone to sway from wind, either nature or forces from oposing trucks
A short trailer tracks closer to your truck's foot print
A long trailer tracks deeper, easier to hit curbs, posts, trees etc.
A long trailer will sweep outward with the rear corner as you start a turn (easier to hit gas pumps and parked cars when initiating your turn)
The closer your hitch is to the rear axle of the tow vehicle makes it more stable traveling forward, but makes you work more when backing.
The more length between your tow vehicle rear axle and your trailer axles, the easier it is to pull, so long as your wheelbase is long enough to support the length.
A long trailer on a short wheelbase truck is more likely to jacknife than a truck with a long wheelbase.
Again, these are my opinions supported from my experience alone.