I've never had to rely on a wheelchair, so I may be incorrect on some of this.
It seems to me that a wheelchair with a person in it may be likely to move around a bit.
If so, a stationary tripod may be more effective than a clamp or arm added as an addition to your wheelchair.
The clamp or arm might be a convenient compromise - sort of the same benefit as you might get from a monopod.
Have you tried using a tripod lowered to a convenient height? Depending on how your chair is configured, and the flexibility that is available to you, you might have difficulty getting close enough to your camera when it is on a tripod - the legs can get in the way of your chair and vice versa. If that is a problem, you may need to look for a tripod that has legs that spread out less, although that can reduce the effectiveness of the tripod.
This is a perfect example, I think, of a situation where you need to try out something, before you buy. Do you have any friends who would let you try out a tripod?
Assuming that a tripod works for you, you may also want to consider issues like the size of the tripod, and how easily it might be carried on your chair.
Also be wary - there is a wide variety of controls and adjustments on tripods. Depending on your circumstances, you may find some much easier to adjust than others.
I too have some physical limitations (limited strength and dexterity in one hand), so I am particularly careful to make sure that the equipment I buy suits my needs.
With all this in mind, it is probably the case that the question you should ask yourself is not "what is the best tripod" but rather "what is the best tripod for me".
Good luck!
Matt