If most people are here for the medium to long term outlook isnt is BTC
which will provide the biggest ROI?
It depends on the people itself how they will managed their respective portfolios. We have different ways and strategy in reaching our ROI whether trading bitcoin or altcoin. Since the goal is to make profit then definitely both methods are capable in getting big ROI.
Strategy is a must and proper analyzation. Without it, no success in getting ROI in both doing trades between BTC or Altcoins.