Should i send bitcoins to hash160 or normal address I am a bit confused here. 
I know that a public address is generated from the private key which you should keep secret, or else, anyone who has it will be able to spend the coins "in that address".

However, when i was checking this link:
https://blockchain.info/address/dd9c56410b2e734e551fc34331a056b70e939c98
containing the hash160 address, blockchain.info showed me that the address from which this hash160 was made is the following: 1MCmcsjzocP68LyBZznA3tjRMvGd4eQRx1
However, if i navigate to this link: 
https://blockchain.info/address/3MtnYRESMWhUDWfch6SkUX6MWSZLcYpRc1
blockchain.info will show me that the hash160 generated from the address : 3MtnYRESMWhUDWfch6SkUX6MWSZLcYpRc1 is the same as the one generated from 1MCmcsjzocP68LyBZznA3tjRMvGd4eQRx1. 
I know that hashing is not a one to one function, it 'is' a many-to-one function but in this case,
My sub-questions are the following:

1) is it possible to get the real address (e.g : 1MCmcsjzocP68LyBZznA3tjRMvGd4eQRx1 or 3MtnYRESMWhUDWfch6SkUX6MWSZLcYpRc1) from the hash160 address (dd9c56410b2e734e551fc34331a056b70e939c98)?

2) why is blockchain.info showing me the the address of the hash160 (dd9c56410b2e734e551fc34331a056b70e939c98) is 1MCmcsjzocP68LyBZznA3tjRMvGd4eQRx1 and not 3MtnYRESMWhUDWfch6SkUX6MWSZLcYpRc1?
Both P2SH and P2PKH use HASH_160. That's what the h stands for in them.

Each HASH_160 is valid in both addresses. As to which address you need to send your BTC to depends on if you are using a redeem script or a public key to spend it.

If you send it to an address starting with 1, your output is encoded as OP_DUP OP_HASH160 &lt;PubkeyHash&gt; OP_EQUALVERIFY OP_CHECKSIG. To spend this, you require a private key that leads to the public key to which the hash belongs, and sign the tx using that.

If you send it to an address starting with 3, your output is encoded as OP_HASH160 &lt;RedeemScriptHash&gt; OP_EQUAL. In this case, to spend the output, you need to provide a redeem script for which the HASH_160 equals the one used in the address (along with any information that the redeem script might use, such as the signatures for a multisig address, or witness for a segwit address).

Due to this, each HASH160 can effectively be used to generate two addresses. Blockchain.info defaults to showing the 1-address. 

DO NOT send any coins to the 1-address if your original address was a 3-address, and vice-versa. You will not be able to recover them.