Is there any coin which can give or is giving a tough competition to Bitcoin ?
Actually, there are many which give competition or are better than bitcoin in technology, but in terms of market cap ethereum is at the 2nd place so you can consider it as a big competitor. but bitcoin has the advantage of 1st cryptocurrency which will always stay with it and it is unlikely that anyone will take place in bitcoin at least not at the moment.
So just buy bitcoin and put some money into good alts too which is going to be huge in future.