And is it possible that for me personally, metta provides more concentration?
When doing breath meditation your mind is relatively more passive where you watch the breath. When doing the four immeasurables your mind is more active contemplating.
Therefore you can maintain your concentration and blocks out distraction as you refocus on different being.
I'm especially curious of this subjectivity aspect in Buddhism. Given the focus on empirical evidence promoted by the Buddha, how does one know / deal with aspects of the path that may be different because of one's own mental disposition? More specifically, how would I ascertain if perhaps some aspects of the path are more difficult to me personally, and whether another way of proceeding would be more beneficial? How do I know what is essential, and what is peripheral?
This knowledge is only available to the Buddha. But through trial and error, one may find practices hard and some more easy and fruitful.
- The Tathagatha Buddha has realized in the exact way how a person’s abilities develop, how they deteriorate, and accordingly their potential to realize the Dhamma. This is His Sixth power.
Source: The Supreme Buddha with His Ten Powers
Also one can use the following as a guide:
The Pali commentaries further provide guidelines for suggesting meditation subjects based on one's general temperament:
- Greedy: the ten foulness meditations; or, body contemplation.
- Hating: the four brahma-viharas; or, the four color kasinas.
- Deluded: mindfulness of breath.
- Faithful: the first six recollections.
- Intelligent: recollection of marana or Nibbana; the perception of disgust of food; or, the analysis of the four elements.
- Speculative: mindfulness of breath.
The six non-color kasinas and the four formless states are suitable for all temperaments.
How do I know what is essential, and what is peripheral?
The dhamma preached by the Buddha does not need anything to be added or taken out. (Svakkhato) Therefore, there is nothing peripheral of not important.