For any latency-sensitive application, we recommend you use orderBookL2. Note that it pushes the full L2 orderbook so the payload can get very large.
OrderBook10 pushes the top 10 levels on every tick but transmits much more data. It's also currently not throttled, but may be in the future.
OrderbookL2_25 provides a subset of the full L2 orderbook, but it is throttled. It gets updated every 100ms.