One name you will surely come across as you compare stairlifts is Acorn. This brand offers a range of stairlifts for various needs - it even produces one for use outdoors.
Acorn says that the Superglide Straight Stairlift is a popular model and claims that its eight rollers and rack and pinion drive offer a particularly smooth ride for users as well as gentle starting and stopping.
Since it is battery powered, it will work even when the mains power fails.
If your staircase is curved, Acorn Stairlifts has the Acorn 80 Curved Rail Starlift, which fits to the stairs without damaging the wall and is promised by the maker to offer as smooth a ride as the straight stairlift.
These are the standard products, but if you have a narrow staircase or stiff knees, Acorn Stairlifts also offers the Superglide Perch model. This shares many of the qualities of the others, but allows you to stand during the ride.
Finally, the Acorn Outdoor Stairlift is made to be shielded from the elements, preventing heat damage or fading.
Acorn Stairlifts all share several features, such as not being cable hauled or having trailing cables, which the maker says provides a smoother ride.