I have 29er Singlespeed that I ride with 2 setups. In fact I have run with 3 in the past
29x3.0, 29x2.6 (35mm wide rims), 29x2.3 (21mm wide rims)
Of the 3 the 29x2.6 is really fun. Good for lots of general riding, but not really as fast as 2.3. I really liked 3.0 for the amazing roll over, but I had to run a rigid fork. Counteracted with weight compared to the 2.3, but I just could not get along the rigid fork. I am just not a rigid fork guy. I could fit in the 2.6 under my 100mm Fox 32 Step Cast fork and found that to be great set-up. Not super light, but great roll over, great traction, and feels like maybe 1" of suspension travel in the rear. Great for riding most places. However wheels and tires are heavier than my 2.3's and so for racing or really smooth trails the 2.3 feel faster. As for tires 3.0 were WTB ranger Light, 2.6 and 2.3 are XR2.
My XC race bike (100mm fr / rear) uses 29x2.35 front and 29x2.2 rear (have a spares at 2.4 F /2.35R when these wear out) and use 24mm internal wide wheels. For this bike this I great set-up.
My AM/Trail/Enduro bike however runs 29x.26 on 35mm internal wheels. That bike has 160mm travel front and 145 rear and want the big tires for grip and roll over. I ride mostly loose surfaces on that bike.