Is Nikon 70-210mm lens better then 18-70mm?
When shooting at subjects far away from you, yes. Otherwise, no. Each lens has its own purpose. Its purpose is dictated mainly by its focal length (the numbers in mm). Want to know more about it? https://keerok.wordpress.com/2014/12/17/what-is-the-best-lens/
You are comparing 2 completely different things with different uses. Either may be better for what they're designed for.
better at what? the 70-210 will have a poor Lower F-stop. the 18-70 has many versions, the lower the f-stop the better the lens in terms of choices of what it is capable of. which all costs more money. a 70-210 is big n heavy, the 18-70 is smaller and lighter. the closest focusing distance may be important for macro work.
Depends on what focal lens u do need
18-70 is better all around lens. The other lens is best for sports and nature.
When I bought the DSLR I wanted, I made sure it came with both 18-55mm and 50-200mm. While the shorter lens will be used most often, the longer is VERY useful for subjects at a distance. Your question is a bit like, "Left or right shoe ?" You need both.