Duration, altitude and season matter more than difficulty grade. Here is how to read a trek page before you book.
Most people pick a first trek by name recognition. A better filter is the shape of the trek itself.
Start with maximum altitude. Anything under 12,000 ft gives your body a gentle introduction, and the difference between 12,000 ft and 15,000 ft is far larger than the numbers suggest. Then look at the longest single day: a trek with one ten-hour day is harder than a trek with five six-hour days, whatever the grade says.
Season decides what you actually see. The same ridge is a green meadow in September and a snow field in January, and the gear you need is completely different. Finally, read the itinerary for acclimatisation days. A route that gains height slowly is not a slower trek — it is a safer one.