We drove when we moved from WI to Portland last year with our (then) almost 2year old. Not horrible, but I wouldn't necessarily recommend it. Every child is different, but for her 2 hours in the car, max really slowed the progress. We'd drive for two hours, stop for 20minutes to an hour, drive two more, stop, etc. She dreaded getting back into the car.
Now that she's a year older she's better, but after 3 1/2 hours she wants out. She also refuses to pee in a pull up or diaper, so if we're traveling more than an hour away the mini toilet training potty goes with us. I imagine we're quite a sight on the side of the road

. I love road trips, but with the great deals we're able to find between PDX and SNA, flying a no brainer. Do you have an Alaska Air CC? The $119 companion fare is pretty great, and when you open it you get a bonus 25,000 miles. Using the two together we paid $350 round trip for three seat for our trip next week. If you figure in round trip fuel, hotel accommodations on the road for 2 extra nights, extra meals for 4 days (2down, 2back up), plus the 4 additional days time it would take, vs 5 flight hours total, my vote goes for flying.
We'll definitely do road trips, but not likely until our youngest is 5 or 6.
Decongestants taken between 1-2 hours prior to boarding will help tremendously with sinus pressure pain. Dum drums help a lot, too. We fly with a mega container of ear plugs (around $10 at Target), and pass them out to anyone in our seating vicinity preflight, "Just in Case." 99% of people are very understanding, especially if you're open and honest up front (ie, Hey folks, this is little Mikies first flight and I have NO idea how he's going to do, we appreciate your patience and understanding. Now, who wants FREE earplugs!?).
I guess I'd rather have to comfort my kids for 2 1/2 hours than have to say, "In six hours we'll be there, please stop crying."