Did you wear out your rear tire, or are you looking to achieve a different handling dynamic? Generally, if running a different front and rear tire, most folks run a tire with better grip in the front and a faster/better rolling tire in the rear. This achieves a more balanced/predictable/safer traction level - you want the rear to loose traction first.
If you are simply replacing the rear because it is time, best bet is to either match the front or find something with smaller knobs/narrower than the front. Or you could slide the front to the rear, and look for something even grippier for a new front tire, if you are looking for more grip overall.
If you want a different handling dynamic, small changes in tread pattern/rubber compound can make huge changes in overall traction behavior. It is worth a read up in the wheel/tire section for general tire characteristics, and you might be able to find some good info in your regional section about which tires work well in your area/conditions.
Also keep in mind that riding style has a big impact on tire performance, as does setup - tubes vs tubeless, pressure, rim width, etc.
Good luck!