mi-17 aren't being phased out as india recently ordered over 80 mi-17IV, which is also known as Mi-8MTV-1, to replace aging mi-8s. Which confuses me though. if buying new birds, why not go for newer model?
IMO india shouldn't go for Chinook as it's work can equally be done with Mi-26 if Chinook too comes with strings.
On the other hand we need either apache, Super Cobra when it is offered or at least Eurocopter Tiger, if attached strings are proved to be too unbearable. We need a tank-killer. PA operates close to 40 cobra and in a future tank battle these birds can be decisive. LCH is not in pipeline yet and even when it comes it's killing power wont be anywhere close to apache or super cobra. LCH would have different use, as due to its light weight and service ceiling, it can operate in extreme heights, like in Ladakh, where Apache or Cobra can't operate with armload.
C-17 would be overkill IMO. It's hideously expensive and price does matter here as India doesn't yet need a strategic airlift. It is still few years when India may play international ball in a big way where it's IL-76 wont be able support or a a/c with more payload may be needed.