As I have had quite a lot of experience on both a geared 29 and a geared 36, I thought I would do an updated write up for those of you deciding on what size wheel to put the hub in.
FWIW: I went from a geared 29er -> geared 36er - > geared 29er, I have over 1,000 miles on the geared 36 and a little less on the geared 29.
Here is my summary:
Geared 29er: More versatile, travels a lot better (flying, driving, etc), if I were to only have only one unicycle in my collection - this would be it (with dual hole cranks). For the road - I put on the Big Apple tire and either use 125 or 150 mm crank slot. On the road, it really only has one useful gear (for most areas). Switching to low gear from high makes it feel like a toy, BUT for long climbs up mountain passes, the low gear is extremely useful. In DC I found myself almost never using the low gear on the road, but now that I have moved to Colorado, the geared 29er is amazing.
Off Road: I put on the Navegal knobby tire, and use 150mm crank slot. This process of switching tires and pedal location took me…20 min or so, but part of it was spent finding the right seat height. For most single track I just leave it in low gear, but if it is smooth enough riding single track in high gear is extremely thrilling! The high gear off road comes in handy when riding on fire roads, or gravel roads to the trail. I was just out in Boulder and found myself actually using both gears off road quite often since the trail I was riding had a lot of easy sections in between the interesting ones.
Geared 36er: The fastest uni for the road for most conditions. The exception would be a race that had a lot of steep climbing (like a lot of races here in Colorado) - although that depends also on how many miles are spent descending. The geared 36er feels like a heavy bike, it isn’t as squirrely as the geared 29er and on the road it has two usable gears for a lot more conditions than the geared 29. Geared 36er simply rides much smoother than a geared 29. The geared 36er is kind of like weight lifting sometimes, it requires a lot of leg strength, and is sure to build up your muscles.
Off road: the geared 36er is great on gravel roads and you can pop it into low gear for stuff that you already do 36er muni on. It rolls over stuff smoothly, and is fun on easy-moderate XC stuff. It is definitely not as versatile off road as the 29er with a knobby tire though.
In Conclusion - If you primarily ride on the road and you don’t live in a mountainous area the geared 36er is the best choice for you. If you simply can’t imagine not riding a 36" uni, the geared 36er is also the choice for you. The 36er really is an amazing ride, both ungeared and geared.
If you want a uni that is an amazing XC/road ride and is highly versatile, get a geared 29er with dual hole cranks. It is amazing being able to go somewhere with one unicycle and 1 extra tire and be able to ride almost anything. If you live in a mountainous area, and ride on the road and frequently climb mountain passes, the geared 29er is also the choice for you. Back in DC, the geared 36er was so much fun, but out here in Colorado, I think the 29er is better because climbing is a breeze on it.
Also - if you primarily do shorter rides on the road (<25 miles) the geared 36er may be better for you as it will give you more of a workout. I find the geared 29er or an ungeared 36er easier to ride on endurance events. Of course some may disagree, as Sam/Roger did their 100+ miles a day for a week ride on geared 36ers, but I found the geared 36er to be quite brutal on a long ride.