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Retail gas station owner Sunoco LP (NYSE:SUN) certainly catches the eye of an income investor. With a yield approaching 15%, its payout could provide an investor's portfolio with plenty of cash flow -- if the company can maintain the payout, which is a big if these days. Because of the concerns surrounding the payout's sustainability, investors are better off forgetting about Sunoco LP and considering Energy Transfer Partners (NYSE: ETP), Williams Partners (NYSE: WPZ), or Valero Logistics Partners (NYSE: VLP) instead. Here's what makes them better dividend stocks.

Keeping it all in the family

Energy Transfer Partners currently is the majority owner of Sunoco LP with a 50.8% stake. It acquired that position via a series of drop-down transactions whereby Energy Transfer Partners sold its retail marketing business to Sunoco LP for cash and units. Because of that arrangement, it would make more sense for investors to buy Energy Transfer Partners because it gets control of Sunoco LP plus access to the midstream giant's other assets.

That said, the Energy Transfer Partners of today should look a bit different in the future after it merges with fellow sibling Sunoco Logistics Partners (NYSE: SXL). While that deal will result in a reduction in Energy Transfer's payout to Sunoco Logistics' current rate, the combined entity will have a stronger balance sheet and growth profile. In fact, those improvements position the new Energy Transfer to deliver double-digit distribution growth over the near term while lurking danger could send Sunoco LP's payout much lower.

The almost step-sibling

In late 2015, Sunoco LP's parent company, Energy Transfer Equity, agreed to acquire fellow midstream general partner Williams Companies (NYSE:WMB) in a cash-and-stock deal. Doing so would have brought Williams Companies' MLP, Williams Partners (NYSE: WPZ), into the Energy Transfer Equity family. However, that deal fell apart earlier this year, which forced Williams Companies to go it alone.

Williams' go-forward strategy included cutting its dividend to provide capital to Williams Partners by supporting the MLP through a major expansion phase. That decision enabled Williams Partners to not only maintain its lucrative payout, but position it to resume growth in 2018. Those efforts should also lead to a significant improvement in Williams Partners' balance sheet, enabling the company to maintain an investment-grade credit rating, while Sunoco's credit remains junk-rated.

Image source: Getty Images.

The middleman

Another of Sunoco LP's issues is the volatility of its cash flow. For example, last quarter adjusted EBITDA was $188.9 million compared to $253.7 million in the year-ago quarter. Driving that decline was lower fuel margin in its retail and wholesale segments. That cash flow volatility is one reason why the company's leverage metrics have deteriorated this year, which put its distribution at risk.

Contrast this with Valero Logistics Partners (NYSE: VLP), which gets 100% of its revenue from fee-based contracts. Instead of earning a fluctuating margin by selling gasoline to retail and wholesale customers, Valero Logistics Partners earns a stable fee by storing and transporting gasoline and other refined products from refineries owned by its parent company, Valero, to retail gas stations. Those fees provide very steady cash flow, and when combined with Valero Logistics Partners' low leverage, put its payout on solid ground.

Investor takeaway

While it is possible that Sunoco LP could maintain its lucrative payout, the company's weak balance sheet and cash flow volatility might leave it with no chose but to reduce the distribution. On the other hand, the payouts of Energy Transfer Partners, Williams Partners, and Valero Logistics Partners are either already on solid ground, or show sure signs of heading in that direction. That's why income investors should forget about Sunoco LP and consider those safer payouts instead.