When Cray went out of business, Sun and SGI got what was left. Was shortly thereafter Sun came out with the 10K. SGI has consistantly beat Sun in terms of raw computing power, but Sun has always shone through with good reliability and modularity.
But, like someone said above...whatever gets the job done. I don't believe in locking myself into one particular solution, so I try to always leave myself a migration path, if needed, to bigger stuff.
But, for a lot of jobs, Linux on a PC works good enough.