On road trips, I wear Tena Supers. They can take a decent flooding and you can continue to dribble or slowly release until you can find a rest stop. They have worked out great for me. They're moderately thick but are really comfy, have a woven shell and velcro tabs that work great, and are fairly discreet with loose pants, but at the same time offer great protection. I have used them on many a road trip with great success. Haven't had much success with any kind of pullup unless you fill them *really* slow. They're just not reliable for sitting mixed with lots of peeing. I do use them at other times, when I am out and active and need something to use very discreetly, but the capacity is no comparison. I have had the best luck with these, here are some links where I buy them from.
Tena Super
http://www.northshorecare.com/tena-super-night.html
The Tena Extra Pull up
http://www.northshorecare.com/pullons-tena.html
I also like Tranquility ATN's because of the capacity and feel, and Tena Flex Briefs. The flex I would not use when sitting for extended times, but they feel great because of the style.
http://www.northshorecare.com/tranquility1.html
http://www.northshorecare.com/tena-flexi-briefs.html
Overall, I have to say the Tena Supers are the only diaper I can rely on for hours of driving comfortably and dry.