Hidden realities of UC vs RTM for downsizing

Resale of my old house is almost done, and now we're looking for a smaller, manageable 2BHK in Noida. Kids have moved out, so don't need such a big place anymore. My budget is around ₹70-80L. I'm quite confused between under-construction projects by builders like Godrej or ATS in Sector 150/78, or a ready-to-move-in flat. RERA delays are a significant concern for UC. Are there hidden maintenance issues or undisclosed costs with RTM properties? Also, hospital proximity is crucial for us. Any advice on which sector or builder offers reliable, low-maintenance societies?