I found a really nice mare the other day. Her show name is Celt's War but her barn name is Coco. Coco is a friesian/saddlebred cross with a lovely smooth stride. She is 15.2hh,a little smaller than I wanted, and 8 years old. Coco is very sweet and is totally bomb proof. Here is a picture of her:
Missouri fox trotters are really good trail horses since they're one of the more sure footed gaiters. They can also make good cart horses since they're stocky, and the foxtrot is meant to cover a lot of ground.
I agree; if you're planning on just pleasure driving in light harness, you'll have more than enough pulling power at any gait of a gaited breed. The diagonal gaits are perhaps more powerful for pulling, but at just 1-2 folks in a light carriage or cart, you'll be fine at the foxtrot or running walk. And some of the gaited breeds can also do the diagonal gaits - my TWH has a to-die-for smooth trot and I plan to break her to the cart someday.
Another idea I would suggest if the Friesian cross doesn't work out for you is to look at Morgans with foundation bloodlines - tucked in there is often the gaiting ability for the single-foot, a lateral four-beat gait similar to a running walk. And, Morgans can't be beat for driving - they're bred to cover ground. Maybe the best of both worlds and a gorgeous animal to boot.
As a new owner of 2 Peruvian Pasos, I need to put a plug in for them too. Super, super smooth. VERY durable--almost always barefoot, and prefer pasturage to stall. I have ridden both Paso Finos and Peruvians and I feel the Peruvian's gait works better for me--steps out more, covers more ground, and more endurance than the Paso Fino. That's just for me--others might say different. But whoever said look at what's in your area--only if you have no choice. I found "my boys" over 4 hours away and drove there twice before buying them to test ride them. The horse you're looking at is gorgeous---if it's smooth and sound and you feel the tug, go for it! Good luck--I am totally in love with gaited horses! Best decision I ever made, besides marrying my husband. :)