I have Ledger Nano S instead of Trezor,Should I buy Trezor or Nano S can also be used to store btc?
Mycellium and Ledger are fine.
If everyone who cares will withdraw and put the bitcoins into trezor, and just sit back and watch the show for a few weeks, who will decide which chain will be the winner at the end?
There is no universal decision. Bitcoin is about individual sovereignty, not democracy or dictatorship or whatever. Nobody can decide for you unless you give up your freedom/control by using a bank, etc.
If a split happens at all (which is uncertain), probably it won't be anywhere near a 50-50 split economically. One side will be a tiny minority both economically and in mining power, and this will be apparent only hours after Aug 1. For example, if I can find hardly any sites that accept one side of the split, and the market value of that side's coins is very low, and too few blocks are being produced to realistically transact on that side, then that one is almost certainly not going to survive in any economically-relevant way, and I'll probably call the "all clear" in 12-24 hours.
In the (IMO very unlikely) event that it's a closer split than that, then we'll need to give instructions for choosing a side (or using both) and splitting your coins, as both sides will have value and will probably exist independently for while, possibly indefinitely. Depending on how things look, I might immediately call one side the true Bitcoin for purposes of categorization on bitcointalk.org, or I might leave it undefined for some days to see how things develop further. Though the other side can continue to exist even if categorized by me as an altcoin, of course.
