What is better to recite diff surahs in wajib namaz after alhamd or the mustahab given in tawzee ie. 1st rakat qadr n 2nd rakat tauheed….in order to improve concentration n obtain benefit of other surahs I wanted to recite them in my wajib daily prayers….can I recite them as the 3rd surah?

You are free to recite any Surah of your choice so long as you know the surah by heart although some surahs are mustahabb as you indicated.
It’s actually a good idea to recite other chapters too.