real time number of transactions world wide https://blockchain.info/unconfirmed-transactions?format=json

I have been given an api key, I would like to call the above url every second to count the number of tx in real-time.

I don't think that this though is the best way to do this as the data might be delayed by the response time and I don't like the idea of calling them that often (I would count that as sort-of abuse of service, though I don't know for sure). Also in a call I would have to filter out any tx with the same id that may have been listed in the previous call.

I would prefer to get a list showing all unconfirmed, and to not miss any at all, to see them as they happen.

I was looking at the bitcoind rpc call 'listtransactions'. I think that this would let me count quicker but, I would like to know if there is a way/api that will push me the world wide unconfirmed tx as they happen (so that I am always 100% accurate to count the real time number of transactions world wide). 

Note: I only need to count the precise 'number of'.
You would have to monitor the block chain yourself, like you say I think it would count as abuse if you poll blockchain.info every single second of every day. The block chain is just a database so if you have programming skills or are willing to pay someone with the skills it wouldn't be too difficult. 

There are probably tools out there already that could do this such as libbitcoin, bitcoinj, etc. I'm not sure. You could even modify the official bitcoind client to log every transaction it receives to a database/textfile/whatever.

FYI the listtransactions RPC call will only list your own transactions, not everybodys.