The seller's real estate agent usually chooses the escrow company. Make sure the escrow company is licensed and in good standing with the Department of Corporations by calling (866) 275-2677, or the Bureau of Real Estate at (213) 620-2072.
California Realtor here. Escrow is opened by the listing agent and 99% of the time the seller/listing agent chooses the escrow company. Escrow is opened once there's a contract.