What is a good mountain bike?
There are too many good mountain bikes to mention.
a dirt bike has a motor mountain biking is arguably more "connected" to the trail and nature. it can also require much more excercise. a mountain bike is much lighter, and has less suspension travel dirt bikes are also more expensive, and require fuel decent dirt bike price= very good mountain bike price
There are a few good mountain bikes tires that would suit a 18 speed bike. I would go to a bike store and ask.there's different tires for what type of riding you doing but everyone have their own way they like their bikes from handle bars to tires. There's no best part. It's just what's good for you