That's the question some investors are grappling with following Walmart's announcement that it will begin rolling out next-day delivery for more than 200,000 products. The announcement on Tuesday came weeks after Amazon said it will work toward making one-day shipping the standard for Prime members.
But Oppenheimer's top technical analyst, Ari Wald, has a clear favorite.
"We think the advantage goes to Amazon," he said Tuesday on CNBC's "Trading Nation."
Wald called attention to a chart showing the relative ratio between the rivals' stock performance. When the line rises, Amazon is outperforming Walmart; when it falls, Amazon is underperforming.
After Amazon's rally in the first half of 2018, it spent the second half of last year trading lower, which Wald's team saw as "a correction in an uptrend," he said.
"More recently, we've seen the ratio stabilize and now turn back in favor towards Amazon. It's inflected higher," he added. "We see this as a resumption of Amazon's long-term trend of outperformance. It's probably not necessarily a case against Walmart, but more so that the bullish case is more compelling for Amazon."
Gina Sanchez, founder and CEO of Chantico Global, also preferred Amazon, but not for the same reasons.
Walmart's next-day delivery announcement wasn't exactly surprising given the company's focus on growing its e-commerce segment, but that doesn't mean it's suddenly a shoe-in comparison with Amazon, she said.
"Moving to next-day or same-day delivery is just a step in the next direction, and the cost of doing that for Walmart is actually not that high," Sanchez said. "However, we would argue that comparing Walmart to Amazon really isn't an apples-to-apples comparison because Amazon is more than e-commerce. Amazon has a much broader offering including their web services, ... and that is actually a big growing component that really has nothing to do with the drivers that drive commerce."
As such, Sanchez said she saw Amazon as the better pick but said she wasn't totally sold on the issue at hand.
"We would side with the idea that Amazon is probably a better trade right now, but we think that this whole same-day delivery is unsustainable," she said. "We think that that's just Amazon trying to drive Walmart to spend money that may not need to be spent. So we will see how that pans out. Walmart is astute, they're good at managing their margins, and so if this is indeed unsustainable, we'll know soon."
Amazon's stock, up nearly 23% year to date, was flat in Wednesday's premarket, a day after rising nearly 1%. Walmart shares gained 0.3% in Wednesday's premarket and rose less than half of 1% on Tuesday, following the delivery announcement. The stock is up less than 8% for 2019.