Except Supermicro's remote management stuff locks up and requires a unit reset to get going again. That's hosed us more than once (across different servers, different timeframes, different datacenters, different providers).
Dell's done some dumb stuff, and the newer gen models are a nightmare to figure out (limiting number of disks for no reason, requiring 2.5" on some models but not others). Plus they gouge you to get a functional KVM ($300+?) But they've been far more reliable than Supermicro, in my limited experience.