Post-possession costs: a reality check needed

Everyone glorifies ATS construction quality, but I've heard too many stories about their maintenance charges post-possession. We're selling our big house, kids have moved out, don't need such a big place anymore. I'm looking for a manageable 2BHK in Sector 150 or near Yamuna Expressway. Considering Godrej and Gaursons too. Builder ka track record kaisa hai on actual construction quality after 2-3 years? Aur post-possession society maintenance charges kitne realistic hain? Not sure if these builders become unresponsive once you take possession. Any honest opinions from residents in their projects? We want a peaceful, low-hassle life now.