bitcoin has many technological limitations(1MB size of block, takes long time to process your transaction) and so had been hardforked to bch, btg.
it could only be used as currency since they do not support platform like ethereum does.
currently many icos are based on ethereums, cause they support tokens on their platform.
I think the only benefit of using bitcoin is that it is the very first cryptocurrency and altcoins are exchangeable in exchange because of btc's stability.
how do you think of bitcoin? will it still have much advantages&value as it now has?
That's right what you say. Bitcoin can be a very valuable coin because Bitcoin had been born since the beginning before Altcoin existed. So they really believe in Bitcoin because Bitcoin will always be able to survive anytime. But keep in mind also that now a lot of ICO that uses Ethereum platform. It means Ethereum is also a very nice and promising coin. Bitcoin's future will still be bright but Altcoin also has a good future.