Which should i buy 'stepper or pedaler' arthritis 63 and weak legs

I'd start with a treadmill that can be set to low speeds. My knee cannot handle high speeds.

If you are very overweight then you need a commercial treadmill that has the torque to handle your weight at walking speeds.

I have a Landice L7 treadmill with the commercial power supply (not the home use power supply): I have had this for over 20 years, and all I have every had to do was lubricate the belt every couple of years. Note that I weighed well over 250 Lb when I got that treadmill (although I was not at my peak of 300+); I'm now a bit above 200 lb (ideal weight is likely about 180 lb).

I'm not a fan of cheap exercise equipment. I broke all kinds of cheap equipment multiple times before I wised up and purchased solid built equipment intended to last a lifetime. But, for just starting out it may be worth buying a cheap model as many people never use their exercise equipment for more than a week or two. Cheap works just fine then.

I wouldn't buy anything without consulting my doctor. Do you have osteoarthritis or rheumatoid? And the state of advancement in each of your joints would have to be considered.

Ellipticals put less strain the knees and ankles than a treadmill or stair stepper

Recumbent cycle/exerciser more comfortable to use and sit on, very low impact. Start out slowly for short periods.

Cycle 100%-its low impact, but yeah speak to a doctor.

I'm intrigued so I did a rudimentary google search for you.

Eleptical or biking, least 150 moderate intensity minutes a week, but can be broken into 10 minute periods if you are feeling like you knees are about to snap.

Maybe a walker. Muahah