Attention to the breath: sensations at the nostrils vs sensations at the abdomen, as they relate to serenity and insight

Breath at the upper lip

(most effective even than the tip of the nose but you may choose the tip of the nose also. Traditional Theravada schools accepts either the tip of the nose and upper lip. Webu Sayadaw and teachers influenced by his teaching hold that upper lib is better. Also more consistent with "around the mouth" interpretation of Parimukam found in multiple Suttas in the Theravada Tripitaka)

• Advantages:
  • Orthodox Theravada Interpretation
  • Develops concentration - serenity
  • More in line with many Buddhist masters and traditions (consensus)
  • One interpretation of Parimukam with appear in nearly all Anapana related Suttas is around the mouth. Hence according to this interpretation more consistent with the Suttas.
  • Covers air element, heat (change of temperature of in out breath) element, liquid element (moisture difference in the in and out breath, and perspiration at the base of the nose), solid element (body part - upper lip), sensation (of the touch of the air), and Kaya (body part - upper lip). Hence can be a basis of transitioning to this type of meditation. Also better insight since in combination with better insight.
• Disadvantage:
  • For a some one starting this may be difficult to feel

Abdomen:

• Advantages:
  • Easy for a beginners (as per justification of practitioners of the Mahasi Method itself)
• Disadvantages:
  • Un Orthodox method devised by U Nārada and popularised by Mahasi Sayadaw
  • Does not develop deep concentration (concentration can accelerate you development of insight.)
  • Progress is slow as interpreted by Buddhist masters advocating the nose, as the surface area of the abdomen is large
  • Based on general justification of the abdomen (from some of the practitioners from the Mahasi Method itself) the primary discriminant is the air element. A careful manuring so it does not contravene the commentaries as observed by traditional and orthodox Theravada masters. At least there seam to be some Mahasi method masters who do not hold to the traditional justification by this linage.
  • This tradition is considered unorthodox and controversial my some Buddhist master (See Banthe Vimalasiri's videos on the Vissudhi Magga and Mahasi Method)

(Following is directly from the Theravada Suttas. So compatible with any tradition which accepts the Theravada Tripitaka as the doctrinal basis.)

insight and serenity goes hand in hand. In Anapana Sutta the 5th and 6th steps in the 4 steps dealing with sensations has serenity.

The 16 Steps of the Anâpāna,sati as satipatthāna

The 12 steps for getting into dhyana [mental absorption]

[Contemplation of the body]

`Step 1—Experiencing a long breath

Step 2—Experiencing a short breath

Step 3—Experiencing the whole breath (or whole body)

Step 4—Calming the breath`

[Contemplation of feelings: Entry into dhyana]

`Step 5—Arousing joy

Step 6—Arousing happiness

Step 7—Understanding mental functions

Step 8—Calming the joy and happiness`

[Contemplation of the mind]

`Step 9—Experiencing the mind

Step 10—Shining the nimitta [meditation sign]

Step 11—Sustaining the nimitta

Step 12—Freeing the mind`

[Contemplation of dharmas]

`The 4 steps to take after emerging from dhyana

Step 13—Reflecting on impermanence (anicca)

Step 14—Reflecting on fading away [of lust] (virāga)

Step 15—Reflecting on cessation [of suffering] (nirodha)

Step 16—Reflecting on letting go [of defilements] (patinissagga)`

Source: The Discourse on the Mindfulness of the In-and-out-breathing by Piya Tan

Upanisa Sutta (read along with Transcendental Dependent Arising A Translation and Exposition of the Upanisa Sutta by Bhikkhu Bodhi), The (eleven) “Without Need of Intention” Discourse - (Ekā,dasaka) Cetanā’karaṇīya Sutta, The (ten) “Without Need of Intention” Discourse - (Dasaka) Cetanā’karaṇīya Sutta and other Suttas covers the formula for liberation (nibiddā formula). Extract from the elven link formulation (formula is more or less the same with minor variations):

`(1) For the morally virtuous (sīla,vata), there arises freedom from remorse (appaṭisāra).

(2) For the remorseless, there arises joy (pamudita).

(3) For the joyful, there arises a zestful mind (pīta,mana).

(4) For the zestful minded, there arises a calm body (passaddha,kāya).

(5) For the calm-bodied, there arises happiness (sukha).

(6) For the happy, there arises concentration (samādhi).

(7) For the concentrated, there arises the vision of true reality (yathā,bhūta,ñāṇa).

(8) For one who sees true reality, there arises revulsion (nibbidā).

(9) For the revulsed, there is letting go [dispassiom] (virāga),

(10) For the dispassionare, there is (10) the knowledge and vision of liberation (vimutti,ñāṇa.dassana)`

Thus implies serenity is important. Also The Great Sixfold Sense-based Discourse - Mahā Saḷ-āyatanika Sutta mentions the need of both Samatha and Vippassana to be developed in a balanced way though the natural development (meditation method and temperament) one may precede the other though ultimately both develop (Yuga,naddha Sutta - The Discourse on the Twin Path).

It really doesn't matter which location you meditate on. The only big difference between the two is that the movement of the abdomen is a very apparent thing while the movement near the nostrils is much more subtle and harder to catch.

The thing that determines if you are practicing Vipassana-Bhavana versus Samatha-Bhavana isn't the location of what you are meditating on but rather the way in which you are looking at the object of meditation. This is clear if one looks carefully at the instructions in Chapter 18 of the Visuddhimagga. Paragraph 5 of said chapter describes Vipassana according to the four elements saying:

5. But one whose vehicle is pure insight, or that same aforesaid one whose vehicle is serenity, discerns the four elements in brief or in detail in one of the various ways given in the chapter on the definition of the four elements (XI.27ff.). Then, when the elements have become clear in their correct essential characteristics...there become plain ten instances of materiality (rupani) with the body decad...

Later in the chapter it is described also in terms of the 18 Dhatus, the 12 Ayatanas, the 5 aggregates, and again the four elements. All of these different categories are classified as being ultimate realities within the Theravada school, whereas everything else is classified as Paññatti, or concepts, meaning that they are mental representations of experiences rather than the experiences themselves.

Thus the only thing that really makes a practice Vipassana meditation is that one is meditating on the object as an experience rather than as a concept. If one is meditating on the abdomen and sets their mind on the physical feelings of the movement themselves, then one is practicing Vipassana meditation but if they are meditating on the stomach itself as being an object, then that is not Vipassana meditation.

Similarly if one is meditating at the nostrils and one is meditating on just the feelings of the air that happen at the walls of the nostril or the lip, that can be Vipassana, but if one is meditating on it just as air moving in and out, that is not Vipassana