IB sends orders for options based upon best price.
Here is the official statement:
Order Routing And Payment For Order Flow Disclosure
IB's Order Routing System: Interactive Brokers offers its customers two primary methods of routing their orders to the market for execution. First, IB customers may directly route their orders to a particular market of their choice. For stocks and options traded at exchanges or ECNs, however, IB recommends that customers use IB's intelligent Best Execution Order Routing System, which is designed to optimize both speed and price of execution. IB's Best Execution system continually scans competing market centers and automatically seeks to route orders to the market center posting the best price, taking into account factors such as the availability of automatic order execution. For securities traded on ECNs, IB also offers "Best ECN" Routing, which will look for the best prevailing price for the customer's order among available ECNs, excluding traditional exchanges.
Automatic Execution and Price Improvement: Electronic Communication Networks ("ECNs") and exchange automatic execution systems generally execute orders instantaneously at the posted bid or offer, rather than routing orders to a specialist or a trading crowd for manual handling. Wherever possible, when an IB customer selects "Best Execution" or "Best ECN" routing, IB routes eligible customer orders to exchanges and market centers currently offering automatic execution of orders. While automatically executed orders do not have an opportunity to be executed at a price better than the market center's posted bid or offer, automatic execution of customer orders is faster and more certain than other methods of execution and eliminates execution of orders at prices inferior to the prices posted at the market when the order was routed to it. IB believes that use of the IB Best Execution System to route orders to the exchange or market center with the best posted price, combined with automatic execution, provides IB customers overall with the most favorable order execution.
Payment for Order Flow: IB does not generally accept payment for order flow for stock orders. An exception exists, however, for certain orders routed to the Island ECN. Island pays subscribers, such as Interactive Brokers, a rebate of $.0010 (1/10th of 1 cent) per executed share for orders that add liquidity to the Island book. This rebate is credited against the fees charged by Island to execute other orders.
IB receives order flow payments in varying amounts from U.S. option exchange specialists and/or market makers pursuant to the mandatory marketing fee programs that have been adopted by the exchanges and approved by the SEC. Receipt of payment for order flow under these exchange programs plays no role in determining where IB routes non-directed customer orders.
Affiliate Relationships: IB's affiliate Timber Hill LLC acts as a specialist or market maker on all U.S. option exchanges. If Timber Hill is a specialist or market maker on an exchange that has posted the best bid or offer for an option contract for which an IB customer has placed an order, and another exchange is also posting the same best bid or offer, IB will break the tie by sending the order to the exchange where Timber Hill is acting as specialist or market maker. Timber Hill LLC is also an active trader of stocks for its own account, and is a registered market maker participating in SuperSOES for certain Nasdaq stocks. IB customer orders can trade with Timber Hill orders if Timber Hill has posted the best bid or offer for a Nasdaq security and an IB customer order is matched with a Timber Hill order pursuant to the execution algorithms used by SuperSOES and the ECNs.