Hiking in India is different from Nepal owing to different weather conditions, varied terrain etc. This post is not to advise which is better but to show the difference in hiking styles to make it easier for you to choose.
The terrain and views:
It is a well-known fact that there are numerous high summits in the world offering breathtaking views, and Nepal has eight out of the ten highest ones. Ranging from Mount Everest to other Himalayan sceneries, hikers get to experience the sunrise and witness the dreamiest panoramic views.
Hiking in India is more diverse, offering different sights and uncovering varied views. This humble abode of the Himalayas is relatively uncrowded, cheap and full of natural, stunning beauty. The rainfall is of longer durations as opposed to Nepal. This changes the natural scenery through different seasons, causes a shift in vegetation and opens avenues to varying terrains. The kind of lush green you see here is not really seen in Nepal.
Trekkers and locals:
In Nepal, hikers get to interact with Sherpas along the way. Depending on the altitude, they get to stop over to have a conversation and meal with them. Besides some of the remotest trekking spots, locals can be seen treading the paths with their stock of food and supplies for the month. In India, however, these interactions are confined to the locals at the base camps, to a large extent.
As far as the concentration of hikers is concerned, Nepal is very popular and witnesses a huge influx of tourists in every year. In India, the scene is picking up, but not all areas are really crowded all year long.
Trekking units of both are well organized, equipped with camping, eating and bathing facilities. Ranging from tours, trekking gear, camping and transport, they have everything taken care of. Shacks serving tea and food are found along the paths.
While internet connectivity can be found at tea-house at regular intervals through most trekking trails in Nepal, this might not quite be the case in India. Besides this, the striking difference lies in the rescue operations. Although the rescue team is growing in India, the one in Nepal is well established. It is expensive, but the units function well.
While most treks in Nepal are Tree-house treks, where you get to stay in wooden tea-houses with easy accessibility of food, hiking in India in similar terrain requires one to carry their own Camping and also make their own temporary food arrangements.
Permits and guides:
Gaining permits while you trek is easier in Nepal. Unless you are opting for a tough trek or are inexperienced, you do not necessarily need a guide or pre-book your trek. Everything can be organized along the way, during working hours only. However, it is advisable to obtain your permits in advance to be safe and sure in both India and Nepal.
If you are looking at clear skies and picturesque views, at tolerable temperatures, the best season to trek in Nepal would be the ones devoid of monsoons or winter frosts, aka the dry season, typically around March to June, and September to November. If you are heading to Ladakh in India, the best time would be after the snow has been cleared, around July or August. Early winter, however, offers some great treks like Sandakphu, Deoriatal-Chandrashila. Keen seekers of the Roopkund trek, please head there around May or June, or September to October.
Both the countries offer gorgeous treks in their own way against beautiful backdrops. When in Nepal, you get to witness the five emerald lakes of the Gokyo trek, remote areas of the Upper Dolpo and the tough camping adventures of the Kanchenjunga amongst many others. In India, you get to see varying terrains while trekking the icy blanket of the Zanskar Frozen River, the Gangotri glacier at the Gomukh Tapovan Trek, the Shepherd Trail Trek, the splendid boom at the Valley of Flowers etc. After all, the intimidating Himalayan range dominates the land of Nepal and stretches across Kashmir to the North-Eastern part of India.