For a short trip (weekend trip or long weekend), Rishikesh is a good place to visit from the plains. You can enjoy activities like rafting, cliff jumping, trekking and temple hopping here. Manali is ideal for a longer vacation (4-5 days or more). You can enjoy activities like paragliding, rafting, trekking and zorbing here or just enjoy a snow fall in the winters.
Rishikesh is good for a short duration trip. Rishikesh is famous for yoga and adventures like rafting and bungee jumping, but rafting is closed in this season whereas manali is a proper hill station , much colder than rishikesh. One can see snowfall in manali .
Depend on your interest. If you have interest in yoga, temples, River Ganges, performing Puja aarti and other religious activities then you must visit Rishikesh. If you have different interest then you can visit Manali. It's totally depend on your interest and priority..!!
Both r good Ashrams temples Ganga Ghaat in Rishikesh ऋषिकेश में आपको बढ़िया व्यू गंगा घाट गंगा आरती मिलेगी मतलब बढ़िया व्यू के साथ एक धार्मिक स्थल है ऋषिकेश मनाली में व्यू बहुत ही बढ़िया यहाँ आपको बर्फ भी देखने को मिलेगी जो ऋषिकेश में नहीं है