MTB Why are 29ers considered better then the legacy 26'' or 27'' tires?
Simple answer 29er wheels roll better that 26" wheels this means better rollover and higher speeds. These are good things for mountain bikes. The trade off is, because they're a larger wheel they require a larger frame. This is especially true for suspension. Usually 29er don't have the same range of suspension as 26" wheels. The larger wheels compensate for some of this on rough ground, but that doesn't help if you're taking large drops.

So really it comes down to what kind of riding you want to do. If you want light trail use and cross-country riding the 29er is ideal. Since you're considering a hardtail I think this is you.