Bluedart - Expensive but very fast and good service. Even rural branches are lightning fast.
DTDC - Expensive, slow, unreliable. It they decide not to deliver then you cannot do anything, you cannot even go to their office and collect. No one will answer your query. DTDC is such a disgrace that sometimes they RTO the parcel the moment they receive it and don't even call and ask if a customer wants to collect himself. These jokers work like govt office, if you are lucky then you can receive a somewhat big packet from one corner of India to another in just 3 days and if you are unlucky then it may take 10 days.
For example, suppose a parcel reaches nearby branch on Saturday afternoon. They won't even prepare paperwork for it, Sunday is holiday. On monday paperwork will be done and Tuesday it will be delivered. That is worse than a Sarkari office. But if it reaches Monday morning then it will be delivered on Tuesday.
Delhivery - Pretty good for the price, nothing can beat it for heavy parcels. Sometimes a bit slow especially in cities but they don't RTO like DTDC.
Delhivery is understaffed, underpaid and overworked that's why they are strained especially in cities.
India post - Very good for small and medium packets. You know where the parcel is and you can collect yourself so that's a plus. Your parcel does not get stuck like DTDC and Delhivery.
Sometimes they throw packets from first floor so use carefully especially in cities.