Servers: Supermicro. Dell in a pinch
Switches: HPE Aruba for 10gig, or Mellanox for 100gig
Routers: I'm not that picky, but I use Fortigate as I scavenged some leftovers at work
UPS: Eaton
Network cards: Intel for 10gig, IBM for 8 or 16gig, Mellanox for 100gig
Harddrives: Exos
RAID stuff: LSI MegaRaid.
GPU: Don't really care, but I have a bunch of NVidia Quadro.
Most of the above preferences are due to scavenging leftover hardware at work.