Both these are top coins so it is best to hold both for long term. Buy whichever one out of these two you do not have or do not have enough of.
This is indeed a very good coin, has its own appeal to lure people to buy. bitcoin is the king of coins and first known to people and many people believe in Bitcoin while Ethereum is the best Altcoin that has proven its ability. Both of these coins are very good and you only need to choose which coins you buy because they are equally good.