Cruiser or Mountain Bike

Well, a cruiser would be better cuz its got smooth road tires. A mountain bike is more durable. It can take the hits and stay in one piece. Then again some cruisers only have one speed. With a 49cc, you'll help the engine along on biggerish/long/some short steep hills. A 66 will only need little help on steep long hills, mostly. Also, take into account the laws in your area. I see your profile says you live in washington. Im guessing you live in Washington state. A mountain bike would be best so if your engine quits in the middle your journey, you can pedal and have plenty of gears to choose from. Cruisers are great long flat journeys. Mountain bikes have knobby tires, so it tends to have more vibration than a cruiser. You could buy road tires and put them on a mountain bike if you want durability and smoothness. Just make sure u get the right size.

I'd use a cruiser for comfort such as long journeys. And a mountain bike for short distances. especially if the terrain started getting a little nasty. Have you thought about a hybrid possibly?
HT=Happy Times. I've heard many reasons why it's called this but don't really care. It's a generic name given to the two stroke bicycle engines from China, any manufacturer. You may have also seen China girl.

I have a motorize hybrid and love it! It's comfortable and pedaling is a breeze with it's multi gears. The bike is light with road tires so the ride is smooth and it hauls @ss!