Deciding which helicopter to buy requires looking at a number of variables. As C&DD say, you want to determine the key mission requirements and some of the "nice haves" to find which model (or selection of models) that will perform the role you need. Then you can start looking at acquisition and operating costs.
Another key factor is delivery times if you are looking for a new aircraft.
As you come from a military background, you may be wise to get the advice of some people with experience in the commercial world, as VIP/Corporate flying has different considerations. And if you do, make sure they have decent experience with helicopters and not just fixed wing.
Good luck