Since I started streaming last year, I've been approached for help from a number of disabled gamers who want to find better ways to play the games they love. I typically say that I'm not really sure what the best solution for them is since everyone is unique, but I always suggest working with their Occupational Therapist to find a system that works for their unique needs. While this is the honest truth, I decided to try and provide a comprehensive write-up on the types of adaptive technology that I've tried or looked into. The following information is purely based on my opinion and information I've found through my research. Additionally, I've found that every game will need a slightly different solution, and the in game settings (keybinds) can be very useful for finding new ways to play a game. My recommendations are based on playing League of Legends since every game may require a very different use of these adaptive solutions.
I've used this type of mouse with my laptop years ago, and I didn't really enjoy it at all. It was hard to have good accuracy and precision, and to do mouse clicks you have to hold the mouse still for a few seconds. I believe you could have external switches mounted to do the mouse clicks, which would make this a decent way of using a mouse for gaming that doesn't need exact precision. This type of mouse usage could be very competitive if a solution for mouse clicking was figured out (likely via switches). Personally, it wouldn't work for me, but I can see it working perfectly fine for others.
I have very little knowledge in this area, but from what I've read, the technology isn't reliable enough for fast-paced gaming. I'd only advise this for someone playing a slower, more casual game.
This technology is our future, but for playing real games, it isn't ready yet. The setup to use the hardware is extensive, and it isn't reliable enough. My sources have told me that it would be like playing with 300-500 ping because of the input delay. I've seen this technology work decently in games where the behaviour of the game is somewhat predictable (i.e. WoW PvE content or single player RPGs), but it would not work very well in games where you face other players because of the input delay.
I've used this technology since it started becoming mainstream years ago, and it has improved a lot since then. Despite the improvements, this technology isn't nearly good enough for any kind of fast paced competitive gaming. Additionally, to make custom voice macros you NEED the Professional version, which has a hefty price tag. I would still recommend it as a compliment to other adaptive solutions because it could easily handle some less critical/time sensitive commands in a game like League of Legends (ward placing).
Trackball or Touchpad Mice
Examples: http://www.logitech.com/en-ca/mice-pointers/trackballs and http://www.ergonomictouchpad.com/
Both these are perfect good alternatives to using a mouse that don't suffer from input lag like the above methods. Whether you want to use these depends on your own personal capabilities and how well you can get them mounted/positioned for you. Your occupational therapist can/will help with this type of device since they are quite standard adaptive solutions.
These are great if you have some movement in your hands, arms, legs, or feet. There are a wide array of switches that vary in size and sensitivity, but this option can be pricey if you need a lot of switches. My current setup revolves around using switches mounted by my foot and elbow to use abilities in League of Legends, so I'm very fond of these.
Best Combination for Adaptive Solutions?
I can't answer that because everyone is different, but I would recommend trying as much as possible, until you find the right fit. I know my own physical limits and ability so well that I found a very good solution for me, but I'm always looking to improve it. For instance, I started playing League with voice recognition software, but I couldn't handle the input delay, so I researched and found the external switches for macro'ing my abilities to. The key is to think outside the box and then see if it exists by googling your idea. 9 times out of 10, someone else had your idea and made it a reality.
I appreciate any comments or input on adaptive solutions that I may have missed. I've tried so much over the years that I'm likely missing a few.