Answer:
Shukriyah or dhanyavad. As far as I know dhanyavad is used all over the India, probobly mostly by Hindu people and shukriyah is more frequently used in north and by Muslim people. As dhanyavad is a word which comes from sanskryt and shukriyah is from urdu but both can be used and both will be understood.
dhanyavaad is a more formal word which comes from sanskrit (dhanya means blessed); shukriya comes from the Arabic word shukran and in India seems to be less formal (though I'm sure it it formal in Pakistan)
Dhanyavaad, it's the "native" Hindi word
Dhanyavaad (native Hindi) or Shukriyaa (Arabic origin)
there is no thank you in the word Hindu