Currently with GEICO, previously it was Nationwide, and before that, Esurance.
it's all highly highly dependent on where you live, what you drive, what demographic you fall into, you driving history, your discounts, etc etc etc.
In general, you'll get a better rate with online-only or online-focused insurers (esurance, GEICO, etc.).
But regargless - no matter what insurer you have now or will switch to, it is to your disadvantage to remain a loyal customer.