This can be really different from one person to another. I personally don`t keep more than 2BTC in a single account. In fact, this is my top limit to risk on trading.

In my case, this is actually %100 percent. But percentage of total funds being used on trading doesn`t exactly mean the person is a big risk taker. It has a lot to do with what you are investing in. I personally wouldn`t buy any altcoin that does not have huge volume on the market. So, it is less likely to make huge profit when you are not investing in a brand new altcoin which you think has a great potential in the future. I hope i explained my point clearly.

No more than 1-2 BTC. i wouldn't advise anyone to hold more than that in an online wallet.

In the past, I've never kept more than a couple bitcoin. Well, except in the early days when it wasn't worth much.

100%.  Otherwise impossible to trade with sell orders. 

Same here. It's too risky. I learned my lesson - you can't trust Bitcoin exchanges.

Yeah. After the Mt Gox scandal, I only keep 5% of my Bitcoin in an exchange. I keep the rest in a trezor.

I keep almost half of my coin in exchange usually in bitfinex and i use 25% of my fund to do altcoin trading. And remaining 25% to use for daily use.

anybody who has been trading for some time, or lost any bitcoin (like me) on cryptcy or couple of others who went down knows not to keep even 1 satoshi on an exchanger or risk losing it.

that is why whenever i trade i withdraw at the end of my session.

You should not put a amount figure on here, the OP wants a perfect strategy based on percentages. I would say, never more than 20% depending on what you own. You could distribute the risk and

use more than one exchange, but it might even expose you to a bigger chance that one of them may pull a Mt Gox on you. If the exchange you are using are regulated, you have a smaller change of

getting Gox'ed. The old saying, " Never invest more than you can lose " still apply to trading on exchanges. Do not go all in... and you will be fine.