Well ideally never put all your eggs in one basket as the saying goes.
 
Both ether and BTC are great long term bets, and you will most likely be well rewarded for holding either of them.
One may outperform the other, but no once can really say these things.

Best to buy both, as for how much of each will that decision is up to you, though i recommend say 70-30 or maybe 60-40 in favor of btc