I do use USB adapters, but more for utility and efficiency than for any sense of authenticity.
I got PS2>USB adapters because my PS3 controller broke, and I have somehow accumulated seven PSX/2 controllers since the late 90s without actively collecting, so it was either $10-$20 for one USB controller or $6 for four.
I also find that the Playstation controller design is the most versatile in terms of how many different control schemes and types of games can be played comfortably. You might prefer an arcade stick or a 6-button pad for fighters or a keyboard/mouse for FPS/RTS/PnC games, but if you had to use one controller for the rest of your life, the Dual Shock has an accurate D-pad, two analog sticks, and enough buttons distributed among your digits to make any console/handheld game at least playable, not to mention a wealth of arcade and PC games that were never intended for a console-style gamepad.