can give some opinion for taipei and vietnam which is better place for backpacker?

Well, In Taiwan you can climb Yushan (Jade Mountain) or Scuba dive off Kenting in the South, Or Wind surf off the Island of Penghu, Or see the Fantastic Toroko Marble Gorges in Hualien where you can also go and watch Whales or Dolphins passing by Taiwan or go White Water Rafting and dip in the open air natural Hot Springs.

If you are under 30, you can join the Youth program here for free. Then if you stay in a Youth Guest house for 3 day , you can get a free train pass to go around Taiwan and see all of the above. Oh!! We also have a lot of Padi fields here!!

http://www.youthtravel.net.tw/

Some people just stay in Taipei and dont really know Taiwan

Definitely Vietnam. Go to Hanoi and Dalang Bay - all of them are in the northern part. There is nothing to see is Taipei - except for the tallest building which doesn't even look that tall. I hated that place, complete waste of my time.

Well, I have done both and I definitely enjoyed Vietnam better. I met some people and we hired a mini-bus with a very good guide/driver and got into situations and experiences in the countryside that were unbelievable. Also, some French travellers in the group were able to get some elderly French-speaking persons to open up to us- and it was great.

Vietnam. There's more to see and discover, and it's much cheaper. Check out this website: http://www.discovervietnam.com.hk/

Taiwan is too developed and expensive, comparatively.