Coming from a bmx background many moons ago i’ve always had a single speed, be it a road bike, fixie or mtb. I never enjoyed it at all on a 26″ MTB. However I now have a 29er mtb, which has made all the difference, really good fun and lots of traction with tubeless tyres. Run with no suspension, steel frame, low pressure tyres, light weight wheels and 32-18T.
Pros:
Having a perfect chain line helps greatly with pedal efficiency.
Being silent is very nice.
Light weight.
Low maintenance all a plus.
Improves technique + fitness.
Will make local terrain far more challenging and ‘alive’ again.
Cheap to run.
Cons:
Yes i do sometime want a lower gear, as a stop start on a hill means walking, which is the worst part.
Spinning out on the flat / downhill.
Riding on the road (due to low pressure in tyres).
If i could only have one bike, a single speedable hard tail, with 1×10 and suspension forks would be my recommendation. Have a single speed rear wheel, quick links on your chain and you can make the switch between gears and hard tail quick and easy.