Google bundles a pair of USB-C earbuds in the box with every Pixel 3 and 3 XL purchase, and the sound quality on offer is pretty decent, all things considered. However, if you're looking for something with a bit more oomph, there are a few options around.
Perfect for Pixels
Libratone Q Adapt
Libratone's Q Adapt are the best option right now if you're looking for USB-C earbuds. The earbuds are designed for the Pixel, they're rated IPX4 for water-resistance (so they're good for workouts), and come with a dedicated button for Google Assistant. You also get a variety of eartips and the ability to select the level of noise isolation.
The Essential HD earphones combine great sound quality with a tangle-free design that makes them easy to carry. The single-button in-line remote can be used to receive phone calls or invoke Google Assistant, and they're certified for hi-res audio.
Xiaomi's USB-C earbuds continue to be a great option in this space. Like the Essential HD, Xiaomi's earbuds are also certified for hi-res audio, and they also feature a titanium-plated metal chamber. The cable is more durable, however, and you get better noise isolation.
There isn't a lot of variety if you're in the market for USB-C earbuds, with audio manufacturers instead focusing on the wireless space. However, if you're not willing to make the switch to Bluetooth audio just yet, then the Libratone Q Adapt is a great choice for your Pixel 3 or 3 XL. They're the only earbuds currently available under the Made for Google program, and the sound quality combined with IPX4 sweat resistance along with customizable noise isolation makes them worth the $149 asking price.