Short term, if Bitcoin forks and drops hard, ETH could temporarily be the leader.

But long term, I think the question is whether one of the alts will really get used.

For ETH, it's not really clear if the "dapp" projects in the pipeline really will get traction. They are hyped, but it's to be seen if they will be used. The most promising for me is Makerdao, although development is slow.

Other alts that bring something new that coud lead to a higher usage are Ardor (interesting "sharding" model with "childchains") and Decred (governance, "hard fork voting").