Ive been using mech boards via PS/2 for a few years now. Basically PS/2 is interupt based where as USB uses polling. The biggest difference though is the ability for PS/2 to accept full key rollover on supported board matrixs (basically any mech board will have full N key rollover, a few dont still however) This just means there is no limit to the number and location of depressed switchs, you could be using all 10 fingers and the system will register all of your requested input (hell you can even cover as much of the board as possible and register the whole thing at once if you had to)
Cheaper USB based boards dont have gaming optimized key matrixs so you may run into issues depressing as few as 3 keys at once. Now days for average WASD configs any gaming focused USB board will have an optimzed matrix so this wont be problem for most users. If you venture into alot of custom keybindings however issues may arrive ( ive seen complaints from those whom run emulators and tend to use thr righter most side of a board)
Switch type is another preference as well. On balance i like my current brown switched board but ive used both black and blue boards as well. Brown is closer to a middle ground of the two where blues are nicer for general typing and blacks for gaming (if you are used to standard scissor or membrane switched boards youll find blacks fatiguing after awhile until you get used to it)
Mech boards have grown substantially in popularity and availability in the last few years so its become easier and cheaper to get one of your liking (as little as 5 years back you'd often need to import one from Asia)
Im a fairly competent typist (80 WPM) and even went as far as buying a board for use at my place of work. Id rather not be subjected to a membrane board if i dont have to be
![Smile :)](./images/smilies/icon_e_smile.gif)
Cool thing about about that when i started there i noticed all the POS terminals had IMB buckling spring boards, there were even some extras still sealed brand new! I thought that was pretty sweet (people still buy those boards on ebay in droves)
(This post brought to you by a 5" touch screen... the irony)