Depends on the car. Usually manual steering will be geared slower to make it manageable at the cost of more wheel-winding. (Old U.S. cars with manual steering would frequently be 5 or 6 turns lock-to-lock.) In general it would be toughest at low speed doing things like parallel parking. Lightest and quickest manual steering would be on a rear-engine car like a Corvair or a VW bug. 

My 1989 Nissan D21 pickup has manual steering. I don't even notice it anymore. As others stated, you have to turn the wheel more at slow speeds, no biggie.

Old question

https://carkiller.com/scottykilmer/qa/cars-with-no-power-steering/

Really depends on the car.. I’ve driven tiny Suzuki’s without power steering no problems.

I’ve also tried to turn the steering wheel of a mid size sedan (engine turned off) while stationary & it was near impossible. I can’t imagine the strength you’d need while parking/3 point turns..

At speed, it shouldn’t really be a problem.

All the early Porsche 911s had manual steering, even with the gas tanks and two batteries in the trunk.  Not a problem once you're under way.