I am not using any other crypto currency at the moment, but I don't think any of them will ever overtake bitcoin. Its the standard of all, its like money now, do you see money competing with anything else? I really don't see that. So I feel bitcoin will hold it own in the market and would probably keep growing.
It is true that no altcoin can overtake the value of bitcoin, though in some terms of technology which altcoin it has more features that is more greater than bitcoin, because there are some altcoin selling a goods like debit card which bitcoin can't do, and because of this things altcoin is helping bitcoin to promote it as well, though it may not increase like the value of bitcoin has it now.