Low cost. Good availability of technicians. Service's remote-control software can regain control after reboot. Friendly, polite staff.
Less thorough service and diagnostic tools than those of firedog or HiWired. No Mac or Linux support.
iYogi is the lowest-cost service I've tested, and it delivers support 24/7/365. But to get what your PC needs, you have to know the right questions to ask and be willing to ask them.