Eth and Btc are the two most potential alts in the marketplace. Both of these alts are surely fine, but I don't think that Eth will replace Btc in the near future. But in addition there still a lot of good alts that traders could try like the Aci coin.
This two coins have both potentials and i think its really good to hold those two coins. But replace bitcoin of ether i think its hard to happen because all those altcoins are relying on bitcoin so never one can replace it. The good thing we do now is hold bitcoin and ether for we get a good profit.