Shall I go for rishikesh or bali
Rishikest for originality.
I've never been to Rishikesh but I have travelled around Bali. Ubud is a yoga heaven and there are some amazing studios there. My favourite was the yoga barn! I wrote a short blog about it, check it out here https://meditatetoliberate.com/2019/01/24/my-top-5-favourite-things-about-the-yoga-barn-ubud-bali/
Enjoy whichever you decide to do!
Rishikesh is the great place for learning the yoga, because it is a birth place of yoga and also known as the world capital of yoga.
Rishikesh is different, it is authentic and your almost all of your teachers are Indian. The culture there is just beautiful, raw, and real. I did my 200 hours in Rishikesh (and have also travelling to Kerala and Goa previously), and I found Rishikesh to be the place where I found myself with a community of like-minded people. It is simple and it is authentic. You meet true yogis who inspire you to live a simple and minimal life.
I feel that Bali is a bit more touristic and focused on a more commercial side of Yoga.
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Bali and Rishikesh both are exceptionally good place for Yoga. Now, coming to your question, you are looking for yoga retreats, right? Rishikesh is the world best place for Yoga Teacher Training as it's the land origin of yoga and almost 90% world's teacher training done in India (especially in Rishikesh). But when it comes to yoga retreats ( Yoga retreat is not only about yoga, it's about wellness and other activities too), so I would suggest you prefer Bali for yoga retreats and Rishikesh for Yoga Teacher Training.