First of all, you can invest in real estate via an Exchange Traded Fund (ETF). Symbol VNQ, traded on the New York Stock Exchange, is one of several such examples. That's not a recommendation necessarily -- it's just an example.
Second, "stocks" are shares of businesses. Those business often own, manage, and otherwise have business interests correlated with real estate. When you're buying shares of stock, you're typically investing in real estate too, to some degree.
Third, I do not recommend investing in only one sector, whether real estate or any other single sector. Stay diversified, at least to a reasonable degree. It's not real estate or stocks. It's some of both, bearing in mind the second point above.
In terms of long-term real returns, real estate has generally not performed that well. (I'm making that statement simply based on the available historical data, which in some places stretches back over centuries.) However, I absolutely agree that tax advantages, government subsidies, and (to some extent) financing can skew those returns. (Financing not really, not directly. Historically that was true, but nowadays the options and futures markets let you execute some crazy, highly leveraged bets if you want. Some countries' tax systems -- the U.S. personal income tax, to pick an example -- provide mortgage-related tax breaks.) So if there are those tax advantages and/or government subsidies, I think they're well worth exploiting. In Singapore HDB is, at root, a government subsidy, whether you're eligible for a grant or not.
Oddly enough, real estate is rather heavily taxed in Singapore, at least compared to other possible passive income streams in Singapore. That taxation obviously cuts down on returns.
