You must first decide if you want a tactile feel or the silent feel. The tactile is the noisy click sound when you depress the keys. The design of the key determines how certain other keys are placed around it, mainly the back slash key and the size of the backspace key. When purchasing a mouse, keep in mind that it must meet your personal preference. The mouse must feel comfortable in your hand.
Trackballs have to fit the same criteria.
Personally speaking, trackballs put my hand to sleep when I use it to play games. Make sure you have easy access to all the buttons and the reach is comfortable. Protect your investment and do not scrimp on the surge protector. The higher the joules , the better protection it will give your system. When you purchase a computer, the operating system should come with it.