On buttons, it feels like Seimitsus have just a touch more resistance than Sanwa buttons. To me, it comes down to the look of the device the buttons are going in, to be honest.
On sticks, I think I actually prefer the Hori Hayabusa over any stick from Sanwa or Seimitsu, but you can't really go wrong with any of them. Stock Seimitsu LS-32/LS-32-1/LS-55/LS-56 springs are a bit stiffer than the stock Sanwa JLF or Hayabusa springs. I prefer a light spring for shooting games, but a heavier spring for everything else.