We use Dell, SuperMicro and Fujitsu.
Dell as usual works amazing, very stable but most expensive.
Fujitsu is an nice surprise, price is better then with Dell, but they are also very stable and functional.
SuperMicro, they are just good. We had most issues with them, maybe because we use them the most...
Anyway, if you ask me which one of those 3 I would choose. I'm not sure.
All of them give some value. See what you need and what budget you have.
Regarding "speed" of some server. It all depends from config you take. You can't go wrong with Intel Xenon series, Dual processor a lot of RAM and HDD depends on use. RAID-10 if you use SATA, but if you want amazing speed there is SSD.
I would say that speed of your server will mostly depend on your budget, not on hardware supplier