HR professional here, been managing company leasing in Thane for 4 years and personally in the market for a 2BHK end-use purchase. Have done extensive research on both Thane and Navi Mumbai. Here is my comparison:
THANE (Ghodbunder Road and Majiwada belt) - 2BHK in the Rs 90 lakh to 1.2 Cr range from established builders - Excellent connectivity: Eastern Express Highway, upcoming Metro Line 4 (Wadala-Kasarvadavali) - Very well developed social infrastructure - R-City malls area, good hospitals, schools - Downside: traffic on Ghodbunder Road during peak hours is a nightmare - Good rental demand from corporate employees (APMC-Turbhe belt companies) - Hiranandani Estate command premium but deliver quality - worth it if budget allows
NAVI MUMBAI (Kharghar, Ulwe, Panvel belt) - Better planned city overall - CIDCO planning shows in road quality and green spaces - 2BHK in Rs 75 lakh to 1.1 Cr range - 10-15% cheaper than comparable Thane locations - Navi Mumbai International Airport (under construction) - once operational this changes everything for capital appreciation in Ulwe and Dronagiri - Kharghar has arguably the best quality of life in the MMR at this price point - Downside: connectivity to Mumbai proper is still a pain - Harbor Line is crowded, Trans-Harbour link (Atal Setu) has helped but not a complete solution
MY VIEW: If you work anywhere in Thane/BKC/Powai - Thane makes more sense. If you work in Navi Mumbai or are okay with a longer commute for a better home, Kharghar/Panvel is the better buy. The airport play in Ulwe is real but it is a 5-7 year bet.
Happy to share specific micro-markets within each if that helps.