A recent Counterpoint Research paper indicated that the Galaxy S10 outsold the Galaxy S9 in the US in the first week by 16%. That same research contained a graphic (image below) that compared the performance of the Samsung phones with the main US competitor, the iPhones. It is clear from the graph, though it stops at the month of February, that Apple outsold Samsung in March as well, if you continue plotting the lines.
That is confirmed by a recent CIRP paper which looks at the performance of the smartphone market for the entire first quarter of the year. Apple, Samsung, LG, and Motorola are the main players who dominated the March quarter, in this exact order. As seen in the image below, Apple outsold all the other manufacturers
Among smartphone brands, in the March 2019 quarter Apple and Samsung led with 36% and 34% of the activations, respectively. LG and Motorola were in third and fourth place, with 11% and 10% of activations, respectively (Chart 2) — CIRP
Up from 2018, but down from 2016 and 2017, Apple managed to grab 36% of the market, followed closely by Samsung and its 34%. CIRP also reveals that in terms of Apple vs the rest, as in iOS vs Android, the Google OS still leads comfortably with 64%, with iOS trailing second at 34% (despite 36% activations in the paragraph above).