It's personal for every person as we all have different standards for how many coins we need to do some trading for example.

But putting that aside, you pointing your focus at the security of an exchange is always a good thing, but nowadays operators performing inside jobs pose a much bigger threat than hackers.

Look at MtGox, MintPal, Cryptsy, it were the operators that have made these exchanges go down with a lot victims as result. I believe Bitfinex is no difference. It was an inside job.

if the exchanger were hacked there's  still a chance for you to recover the loss or the exchangers will be responsible of your loss because it's their fault even they can't fully recover your loss but you will still get your funds,but if the exchanger just turning out scamming people,they will ran away with your money and there's nothing you can do

It is true that never keep your all coins on an exchange.
Because there are some exchange having a problem   

Poloniex is not the only exchange that refunded its users. As far as I remember, BTC-e also refunded users of a minor security breach.

In both cases the funds lost did amount only for a fraction of the funds held. Therefore it was easy to do a refund. So users have been lucky.

I don't think that you truly can distinguish between "reputable" and "other" exchanges from the outside. An exchange is only "reputable" as long as it is not hacked. There is never a guarantee that the system is as secure as it is claimed to be and that all employees are honest.

So it doesn't matter at which exchange you store your funds, you're still taking a significantly higher risk than storing them in a private wallet which you control.

ya.ya.yo!

Sure i do understand about the funds not being safety at exchanges, but we need them to try to get more bitcoins, in fact those are were the most bitcoins are being invested and traded, if i hold my coins at my wallet im just waiting a better price or something to invest later.

Today I have best tip from here this forum that never keep all your coins on an exchange because I check many biggest and solid exchanges already defaulted and run with too much money and all is unrecoverable those who lost are in deep problems even they cannot complain to any one for this mistake

I had some bad experience when I kept nothing on exchange and I lost some good opportunities so you have to keep something if you don’t want to miss good opportunities. Yes there is risk associated with it but trading is all about risk and if one is not brave enough to take this basic risk then he should not trade further imo.

Yeah right if you dont keep your bitcoin invest in the exchange site you will be miss for some opportunity to buy it but there is other way that you can save them every time you make already a profit those profit better to save it for your safety wallet..  to secured it.. or if you want to increase your revenue better to spread it to other exchange site..  to increase your profit and for safety of your other investment,.

That's also what I am doing. I only send coins to my exchange when I am trading. In the times that I am not trading, I don't have any coins there. Everything sits safely in my offline wallet. Everyone should do this. People that keep their coins sitting in their exchange accounts are not aware of the risks, or they simply don't care and think their exchange won't get hacked.