The best controller for steam deck is one you already have. My PS One Analog is still working, tho through cable with more than a decade old PS2 to PS3 USB converter.
Vienon PS2 to USB Controller Adapter, 2 Pack for Malaysia | Ubuy
For PS1 Dual-shock GamePad to PC USB Games Controller Adapter Converter | eBay
Wireless Controller For PS2/PS1 Gamepad Dual Vibration Shock For Sony Playstation 2 Joypad Joystick Controle USB PC Game Console
OSTENT Blue Dual USB Adapter Converter Cable Cord for Sony PS1 PS2 Wired Controller Gamepad Joystick to PC Laptop : Amazon.co.uk: PC & Video Games
The playstation classic controller just has a micro usb connector in it : r/mildlyinteresting
USB PS1/PC Computer 1.5m Wired Gamepad Game Controller Joystick Rocker LR Black | eBay
Official Oem Sony PlayStation Classic PS1 Mini USB Controller Gray SCPH-1000R | eBay
Official Sony PlayStation Classic Mini [SCPH-1000R] PS1 OEM Wired USB Controller | eBay
Dual PSX PS1 PS2 Playstation 2 To PS3 PC USB Pad Controller Converter Adapter | eBay
PlayStation 1 Classic USB Controller by AdrianoRamosOfHT on DeviantArt
raphnet. - PS1/PS2 controller to USB adapter
raphnet. - PS1/PS2 controller to USB adapter
Can you use real PS1 Controller with PS Classic ? Tried USB Adapter not Work : r/PlaystationClassic
OSTENT USB Adapter Converter Cable Cord for Sony PS1 PS2 Wired Controller Gamepad Joystick to PC Laptop: Amazon.co.uk: PC & Video Games