It doesn’t matter which model you decide to buy: a Mammut harness gives you guaranteed protection. However for long-term satisfaction, it’s important to choose both the right model, and get a good fit. Take your time when you are buying a harness.
Areas of use
Choose the harness appropriate for the type of climbing you wish to do. Set your priorities right. For example, comfortable padding on high alpine tours where you practically never hang in the harness is unnecessary and can often be quite annoying, especially when walking.
If hanging free is a possibility or a necessity for the type of climbing you partake in, then you should be able to judge the fit and comfort by doing a hang test, which is usually offered in climbing specialty shops.
Read the instructions before you use the harness and make yourself familiar with the buckles and other features of the harness
Of course the size can also vary depending on the model of the harness. Thus you should always try the harness on; preferably with the clothing you will be wearing under the harness. A flat hand should fit snugly between the thigh and the leg loops.