Is it better to invest in ETF or unit trust or stock for a regular saving plan?

Unit Trusts / Mutual Funds have (almost) no advantage compared to ETFs.

expensive, underperforming their benchmarks over longer term

Hello! You should invest your money with a long term goal in mind. Among the options you have given, ETF makes sense because of the lower fees paid and it offers you instant diversification, which an individual stock does not grant you.