5 mantra Hindu

#1 Gayatri / Mantra Savitri (Gayatri) Mantra - Most Powerful Vedic:
Rigveda (RV 3.62.10)

In Devanagari script
ॐ भूर्भुवः॒ स्वः ।
तत्स॑वि॒तुर्वरे॑ण्यं॒
भर्गो॑ दे॒वस्य॑ धीमहि ।
धियो॒ यो नः॑ प्रचो॒दया॑त् ॥
In IAST transliteration
Oṃ bhūr bhuvaḥ svaḥ
tát savitúr váreṇ(i)yaṃ
bhárgo devásya dhīmahi
dhíyo yó naḥ pracodáyāt

However, traditionally, the stanza RV.3.62.10 is imparted only to Brahmin boys. Other Gayatri verses are used in the upanayana ceremony for non-Brahmins: RV.1.35.2, in the tristubh meter, for a
kshatriya and either RV.1.35.9 or RV.4.40.5 in the jagati meter for a
Vaishya.

#2 महामृत्युंजय मंत्र, mahāmṛtyuṃjaya Lord Shiva’s Mantra:
Rigveda (RV 7 .59.12).

In Devanagari script
ॐ त्र्यम्बकं यजामहे सुगन्धिंम् पुष्टिवर्धनम् ।
उर्वारुकमिव बन्धनान् मृत्योर्मुक्षीय मामृतात् ।।
In IAST transliteration:
oṁ tryambakaṁ yajāmahe sugandhiṁ puṣṭi-vardhanam ǀ
urvārukam-iva bandhanān mṛtyormukṣīya māmṛtāt ǁ

#3 Vishvani Deva Mantra for Abundance:
Om Vishvani Deva
Svitarduritani Para Suva
Yad Bhadram
Tanna a Suva

#4 Lord Ganesha Vakratunda Mahakaya Mantra for Success:
Vakratunda Mahakaya
Surya Koti Samaprabha
Nirvighnam Kurumedeva
Shubha Karyeshu Sarvada

#5 highest:
AUM (OM)