The Hospitalisation plan you mentioned is an enhanced shield plan. Premium for basic plan via cpf and the rider via cash. The plans in the market are more or less similar except for some features that are unique to the insurer. Aviva for example offers moratorium underwriting which mean that no underwriting is required but should there be a claim,they will check if teh condition is a pre-existing condition. If a specific condition did not require a medical consultation in teh last five years, I think they will cover it if I dont't remember wrongly.
For AIA, there is an additional $100,000 coverage if the admission is due to a covered critical illness and they also cover for living organ donor transplant. This is payable regardless of you being the done or the reciepient of an organ.
Firstly, you should decide the kind of medical needs you prefer such as private or government restructured hospital and the kind of ward.
Hope this helps!