I also grew Copra which is a top-notch keeper and has a strong flavor. I find Highlander to be milder in flavor, not as much as the sweet onions, but nowhere near as strong as the Copras. They're good for cooking and salads. My Copras are a bit smaller than the Highlanders, but considerably larger than the Big Daddys.

Here's a crate with perhaps 1/6 of my Highlanders, tennis ball for scale.

This year we wanted to try Highlander because there are not that many intermediate-day onion options - and Highlander was touted as an early maturing onion. It was a good decision because the onion grew very well here and bulbed-up nicely. You can see the difference between Highlander and the other long-day onion bulbs if you compare them in the photos? The other long-day onions apparently didn't have sun and temperature necessary to complete their growth - the bulbs are narrow and elongated - the necks are thick because we had to pull them to protect them from freezing temps - and like I said - they did not store long!