: I carry up to 4 strippers on their side on my car. No problems. I also find
: the boats easier to load in this position.

It's probably easier to load and unload kayaks on J-cradles on a car. If you're used to solo carrying, the boat is already in position, and you just lift it slightly and set it in place. On a taller vehicle, it would be awkward, since lifting heavy things above shoulder-height isn't always easy.

Horizontal cradles on a pickup or other tall-roofline vehicle, (as Ross mentions, it's not as easy on a 4x4), make loading easier, since you're more likely to load it from the rear.

If you're not strong enough to carry your boat by the cockpit, and commonly carry with a partner, it's easier to load onto horizontal saddles...having two people lifting and turning a boat with upswept ends is comical, frustrating, and awkward.

Shawn