Best place to stay in JKT so that I can explore JKT day & night

Depends what you want.

PIK in the north is growing in bars and restaurants and is pretty busy. Kemang in the south is the same but always crowded but the bars are strung out all over the place. Cilandak Town square is pretty good for the same.
Clubs can be found in Kemang and Senayan area and then for the more darker venues then Block M, Jalan Jaksa and the rest is up to you.
Some of the bigger malls like Central Park or Pondok Indah have a huge variety of things to do, it really depends on you.

However, I would as already advised base myself in the Thamrin area as it is close enough to many places whatever your tastes....