Selling puts against ETFs versus stocks?

I read a good post on a blog that I enjoy - tastytrade, stocks versus ETFs - about trading options using ETFs versus single stocks.  Author Sage Anderson emphasized the different volatility & of course, the different risk.  In my IRA, I sell puts against SPY, the ETF that holds the stocks of the S&P 500 index.  But I've often considered selling puts against individual stocks, to get more of what I call premium yield.  I'm bullish on oil, so XOM (Exxon Mobil, in the S&P 500's top 10) is a stock to consider for selling puts against.  Around yesterday's trading close, I reviewed the November 16, 2018, SPY & XOM puts.  SPY was at $280.42 & XOM was at $81.32.  Unlike Anderson, I don't look at the volatility index.  But I do look at arithmetic because for me, it really quantifies the risk.  I chose the SPY $276 put & the XOM $80 put because they were both about 1.6% out of the money.  Since I'm a put seller, I consider the premium's BID price - $3.01 for SPY & $1.60 for XOM - when I calculate premium yield.  Selling cash secured puts, I must reserve $276 (per contract share) for SPY & $80 for XOM in my IRA's core position.  For selling the SPY put, $3.01 divided by $276 = 1.09% over 30 days, or 13.27% annualized.  For selling the XOM put, $1.60/$80 = 2.00%; 24.33% annualized.  The 24.33% premium yield is very attractive, but I'm afraid of XOM's put selling risk - dropping to $40, or to $0!  SPY's 13.27% premium yield is quite attractive, but I'm not afraid that SPY will tank to $138, or to $0!