What kind of night life are you talking about?
Young people/backpackers prefer Khao San Road. Upscale restaurants/bars are found in Sukhumvit and Ratchada. Around Nana you will find host bars/red light district. Gay area is Silom/Sathon. So it really differs a lot.
Anyway, if you stay in Sukhumvit (Siam, Chit lom, or Ploen chit preferably) it will be a solid choice and you can get around from there by taxi or BTS (or even MRT if you stay in Asoke).