Mantra japa or nama japa for me?

[MahaHrada]

Sorry if I posted my question at the wrong thread. I've been searching for japa mantras on the net and I noticed something.

Om Gam Ganapataye Namah and also some of the Ganesh Siddhi mantras with all ending with 'Namah'. I assume that when reciting, one should say it as 'Na-ma-haa' not as 'Na-ma'?

Yes and No, namah ends with Visarga (H) so it is correct to add the vowel that precedes the visarga, nam-aha- but not prolonged like you wrote (aa) but shortened only half the time than the preceding short (a) which has a duration of 1 matra, the added (a) at the end of namah(a) has only a duration of 1/2 matra.

[SriGauranga]

Hare Krishna. Please accept my humble obeisances. All glories to Srila Prabhupada!
There's a quick solution to you problem, prabhu ji. In this Kali Yuga Lord Chaitanya advised us to chant the Hare Krishna Maha Mantra. He told us that the chanting of Hare Krishna Maha Mantra will give us ultimate love(prema) for Krishna and self-realization. I will present what srciptures tell us about Hare Krishna Maha Mantra(not my work):
Śrīmad-Bhāgavatam [12.3.51] it is said:
kaler doṣa-nidhe rājann
asti hy eko mahān guṇaḥ
kīrtanād eva kṛṣṇasya
mukta-saṅgaḥ paraṁ vrajet
“In the Age of Kali there are many faults, for people are subjected to many miserable conditions, yet in this age there is one great benediction: simply by chanting the Hare Kṛṣṇa mahā-mantra one can be freed from all material contamination and thus be elevated to the spiritual world.”
Nārada-pañcarātra:
trayo vedaḥ ṣaḍ-aṅgāni chandāṁsi vividhāḥ surāḥ
sarvaṁ aṣṭākṣarāntaḥsthaṁ yac cānyad api vāṅ-mayam
sarva-vedānta-sārārthah saṁsārārṇava-tāraṇaḥ
“The essence of all Vedic knowledge—comprehending the three kinds of Vedic activity [karma-kāṇḍa, jñāna-kāṇḍa and upasāna-kāṇḍa], the chandas, or Vedic hymns, and the processes for satisfying the demigods—is included in the eight syllables Hare Kṛṣṇa, Hare Kṛṣṇa. This is the reality of all Vedānta. The chanting of the Holy Name is the only means to cross the ocean of nescience.”
Kali-santaraṇa Upaniṣad
hare kṛṣṇa hare kṛṣṇa kṛṣṇa kṛṣṇa hare hare
hare rāma hare rāma rāma rāma hare hare
iti ṣoḍaśakaṁ nāmnāṁ kali-kalmaṣa-nāśanam
nātaḥ parataropāyaḥ sarva-vedeṣu dṛśyate
“Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare; Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare—these sixteen names composed of thirty-two syllables are the only means to counteract the evil effects of Kali-yuga. In all the Vedas it is seen that to cross the ocean of nescience there is no alternative to the chanting of the Holy Name.”
Śrīmad Bhāgavatam 12.3.52:
kṛte yad dhyāyato viṣṇuṁ tretāyāṁ yajato makhaiḥ
dvāpare paricaryāyāṁ kalau tad dhari-kīrtanāt
“Whatever result was obtained in Satya-yuga by meditating on Viṣṇu, in Tretā-yuga by performing sacrifices, and in Dvāpara-yuga by serving the Lord’s lotus feet can be obtained in Kali-yuga simply by chanting the Hare Kṛṣṇa mahā-mantra.”
Śrīmad Bhāgavatam 12.3.51 it is stated:
kaler doṣa-nidhe rājann asti hy eko mahān guṇaḥ
kīrtanād eva kṛṣṇasya mukta-saṅgaḥ paraṁ vrajet
“My dear King, although Kali-yuga is an ocean of faults, there is still one good quality about this age: Simply by chanting the Hare Kṛṣṇa mahā-mantra, one can become free from material bondage and be promoted to the transcendental kingdom.”
Chant the holy names, chant the holy names, chant the holy names. In this age of Kali [the age of quarrel and confusion] without a doubt, there is no other way, there is no other way, there is no other way. (Brihan-naradiya Purana 38.126)
In this age, there is no use in meditation, sacrifice and temple worship. Simply by chanting the holy name of Krishna--Hare Krishna, Hare Krishna, Krishna Krishna, Hare Hare/Hare Rama, Hare Rama, Rama Rama, Hare Hare--one can achieve perfect self-realization. (Vishnu Purana 6.2.17)
Living beings who are entangled in the complicated meshes of birth and death can be freed immediately by even unconsciously chanting the holy name of Krishna, which is feared by fear personified. (Bhag.1.1.14)
When instructing King Pariksit, the great sage Sri Shukadeva Gosvami said, "O King, constant chanting of the holy name of the Lord after the ways of the great authorities is the doubtless and fearless way of success for all, including those who are free from all material desires, those who are desirous of all material enjoyment, and also those who are self-satisfied by dint of transcendental knowledge. What is the value of a prolonged life, which is wasted, inexperienced by years in this world? Better a moment of full consciousness, because that gives one a start in searching after his supreme interest." (Bhag.2.1.11-13)
Simply by chanting one holy name of Hari, a sinful man can counteract the reactions to more sins than he is able to commit. (Brihad-vishnu Purana)
As when all small animals flee in fear when a lion roars, similarly all one's sinful reactions leave when a person chants the Lord's holy names while in a helpless condition or even if he has no desire to do so. (Garuda Purana)
The path to liberation is guaranteed when a person once chants the holy name of Lord Hari. (Skanda Purana)
In this age of Kali there is no other means, no other means, no other means for self-realization than chanting the holy name, chanting the holy name, chanting the holy name of Lord Hari. (brhan naradiya purana 3.8.126)
Your eternal servant. Hari Bol!

[Purana]

Thank you for your reply and sharing.