We get this question a lot! Those of you who have been riding for a while probably already have clear preferences, so we're going to provide a simplified outline or "guide" to help newer riders choose between the two. When choosing a bike, so much has to do with personal preference, however we do recommend full-suspension the majority of the time based on riding comfort.
When choosing between a full suspension mountain bike or hardtail mountain bike, use your riding style to help determine the best choice for you. Typically, the key points are going to come down to three factors terrain, price and comfort. Depending on the individual possibly not in that order
1. Terrain: Hardtail mountain bikes transfer power more efficiently on non-technical surfaces and uphill climbs. When biking downhill on bumpy trails, full-suspension is usually the clear winner for comfort, traction and preserving rider energy.
2. Price: A lot like selecting a bike, everyone has a personal comfort zone when it comes to budget. Hardtails are typically more economical in both base price and maintenance costs. Full suspension mountain bikes have more parts, more innovative technology and are consequently more expensive.
3. Wheel size: The regular wheels size of all mountain bikes used to be 26" but this changed. Due to the success of the 29" wheel size which accommodates taller riders and gives a better ability to ride over obstacles and rocky terrain a new wheels size was born: the middle between the 2 worlds: 27.5" (or 650b how it's also called). Talk to your local bike shop to find out what is best for you.
4. Comfort: The older you get, the more important comfort becomes to you. I personally used to simply "make do" with many things in life and as I've aged, I've become much less interested in simply making do. I enjoy a little off-road downhill and the full suspension takes a lot less out of me.