MH basic would be the cheapest of all the 3 fares. It is Non endorsable, non transferable and non refundable.Seats are limited and are subject to availability of the relevant booking class.  As it is the cheapest, this will be the bargain if you are absolutely sure about the dates you are flying as you are not allowed to change departure dates to/from destinations. If for some reason you are unable to travel on the date, the whole ticket is gone.  Nothing can be done about it.

MH Smart and MH Flex is having almost the same conditions except that Flex is the short for flexible which means that you can do a lot with the ticket You need to pay fees for changes to this type of ticket.  Its about the same with Smart except that I think MH Flex you can travel on code share airlines and pay a difference if the fare is higher.  Also you can choose your seats for free which for MH smart, you need to pay a fee.  MH Smart is the mid between the 2 fares, is also limited but has more options open if you want to change dates subject to the promotion period/type of aircraft depending on continents unlike MH flex which has no restriction. MH flex because of its flexibility is the more expensive of the 3.  The ticket is refundable subject to penalty fees.

all economy priced tickets will need to pay some fees to change.

the only way to prevent paying fees is to buy either business or first class with full fares.