Back in my village in Punjab, TATA CDMA has great coverage and very good signal-strength while all other GSM/CDMA have coverage bun not much signal strength. Same I can say about smaller towns in Punjab where my friends had TATA CDMA connections. I have used RCDMA for few days myself in Hyderabad and it was no way comparable to TATA CDMA.
CDMA is dying technology when it comes to mobiles, I do not recommend anyone to choose CDMA. GSM is much open and cheaper technology, probably because CDMA is marred by royalty QUALCOMM asks for which makes handsets expensive and even if some company manufactures cheper handsets (like Reliance did in beginning) then they have to share profits in business. This does not end here, littile search in internet will tell you a lot more. Yes, CDMA may have more voice clarity and good signal strength but any open and cheaper technology (in comparison to closed/expensive technology) will find ways to improvise and become better and better and then get ahead of its limitations and then get ahead of strengths of the closed/expensive technology. QUALCOMM already gave up 4G-CDMA (Ultra Mobile Band a.k.a UMB) in favor of LTE because LTE found better way of migrating from both EVDO and 3G. Now LTE-Advanced is here already.
If you are buying a new connection then by all means get a GSM connection and if you already have CDMA then port. You will learn sooner or later why I am saying so