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My first meditation teachers were Zen practitioners who taught me to focus on sensations of breathing as felt in my abdomen. When I trained as a meditation teacher, I was coached to put my attention on the breath at the very tip of the nostrils, the place where the air first touches the body during an inhalation. In some traditions, teachers don’t give any instruction at all in terms of where in the body to sense the breath.
And, there’s more. Some teachers assert that you should gradually alter the breath as you sit so that the in-breath and out-breath are the same length. Others suggest the out-breath should be longer than the in-breath, and others still tell you not to alter the breath in any way.
Buddhist teacher, Thanissaro Bhikkhu says he was encouraged by his teachers to play with the breath. He offers an interesting guided meditation in which he coaches you to notice body sensations as breathe in an out of different quadrants of the abdomen and chest. 
I’ve also tried a form of somatic meditation where I imagined the in-breath coming directly into the lower dan t’ian, which traditional Chinese medicine suggests is an important energy center located in the middle of the abdomen. In that practice, the out-breath was disregarded completely. And currently, I’m reading Shambhala: The Sacred Path of the Warrior by Chogyam Trungpa. He suggests you should put full focus on the outbreath, allowing yourself to diffuse and dissolve with it. Then, the in-breath should happen naturally, all by itself, allowing you to focus on the uprightness of your sitting posture.
So many strategies! Which one is the right one? None of them and all of them.
Zenmaster Thich Nhat Hanh taught me that all meditation is meditation on something. There is always an object of meditation. The truth is, the object doesn’t matter all that much. You could meditate on something you see such as a flower, a flickering candle, or a mandala. You could meditate on something you hear such as a mantra you repeat silently to yourself, or the sounds in your environment. You can meditate on pain, or discomfort, or other body sensations. Or, on emotions, feelings, or thoughts. And, there are forms of meditation, such as open awareness, in which the focus changes regularly depending on what arises in the present moment.
So, if all of these meditation objects are viable, that means that any form of breathing can also become a meditation object. The question remains, though, which one should you choose?
My guided meditations always coach you to “Find a place in the body where you can comfortably and easily notice the sensations of breathing.” I believe this is a good strategy for beginners and something you can continue doing forever. If you choose a strategy that’s easy and comfortable, you’ll find it easier to meditate and you’ll see benefits faster.
The only benefit to choosing a difficult strategy is that it can present a helpful challenge if you’re willing to be persistent and patient. If you stick with something difficult, you may eventually build skills at a deeper level. If the challenge is too strong, however, you may give up and then you’ll be no further ahead. What I’m saying is, leave the challenging stuff for times when you feel you’re up for it.
There’s also some benefit to changing things up periodically or playing with your breath in the way suggested by Thanissaro Bhikkhu. Doing this periodically gives you different perspectives which afford an opportunity to learn new things about yourself.
There are two cautions, though:

* Don’t change things up too often. When you flit from one strategy to another, you don’t ever stick with one thing long enough to fully explore it.