A 10:30am flight gives you plenty of time to take the train to the airport. If you've only got a fraction of a day, Causeway Bay is a good idea. It's every bit as tourist-infested as Tsim Sha Tsui, but is more interesting for someone who's never been to HKG before. If the weather is decent, take a walk in Victoria park. If the weather is terrible, eat.
I used to stay at the Park Lane with family years ago. It's nice and the extra cost for the harbor/park view is well worth it. I stay in Tsim Sha Tsui now for business reasons. If you go that way the Kowloon Hotel is small but nice and the Kowloon Shangri-La is 1/2 the price of the one on the island and has (1) an amazing Chinese restaurant and (2) one of the best bars in Hong Kong.
The Kowloon side has bird street and the jade market, both of which are an easy train ride to Mong Kok from wherever you decide to stay. Going to Victoria peak is a 1/2 day deal and is only worth it if it's clear. The bar at the Intercontinental has the best view of anywhere other than Hoboken. Go there at dusk and see the nightly laser/neon light show over the island.
The first train to the airport leaves at 6:30 and you'll have plenty of time to make your flight no matter what you do.