Both for sale at Costco as of the time of posting, wanted to offer up my feedback on the two and my choice.

Sennheiser Momentum Open

Regularly $90, $30 off, paid $60.

Entire bud is hard plastic, one size fits all. Easily jostled loose when chewing and eating. Fell out when hiking/jogging.

The case was also cheap feeling, the hinge was not strong enough to stay open in any position. The case cannot be placed on a surface and kept open on its back or on its front. It's a little complaint but something Google got right with their A-Series buds many years ago.

The stalks were very sensitive, they always registered a touch on first try. This was both a positive and a negative, because due to their fit, they constantly felt loose and like they needed to be pushed back in, which triggered the pause each time.

Sound Quality: I thought that even with all of the above, they would atleast have better sound quality but unfortunately the bass is VERY boosted. I tested on YouTube videos, podcasts, an audiobook, some pop-punk music. In each case the bass was much more pronounced than intended. It even picked up some low tones from cheap audio equipment from some smaller content creators, actually making me turn them off entirely when using the Sennheiser Momentums.

Bluetooth distance: The earbud also started getting choppy at about 25 feet from the Bluetooth device, 1.5 rooms away.

Battery: went from 40% to 20% in 100 minutes

Soundcore Liberty 5

$70, full price.

Comes with a rubber nipple and also 5 alternative fitment options. The standard ones fit me fine. They stayed put during the same activities (eating, talking, and hiking/jogging).

The case felt better and was sleek. Had a nice light bar to let you know when it was in pairing mode. My phone immediately picked it up when I slid it open.

The stalks and controls were less sensitive. Instructions were not even provided, have to scan a QR code to download the Manual.

The ANC was amazing. Accidentally activated it and the fan in my bedroom completely disappeared. I'll need to download the manual to figure out how to turn it back off because it's too effective for its use case.

Sound Quality: felt true to nature. I skipped around the same YouTube videos, podcasts, audiobooks, and Spotify and everything sounded the same as when I listen from other headphones, Pixel 10 Pro speakers, or my studio monitors on my desk. There was no bass boost which had actually ruined some content on the other buds.

Bluetooth distance: Had to go 3 full rooms and down a floor before the Bluetooth connection started getting choppy.

Battery: battery went from 100% to 80% in about 2.5 hours

Conclusion:

Obviously from this review you can tell I'm keeping the Soundcore Liberty 5s for my use case (listening to audio books while hiking) but I will say that the Sennheiser Momentums could definitely satisfy other people's Use Cases.

If you like Bass Boost for music listening and/or will be using them in an office (need the open back nature to hear your surroundings), the Sennheisers could fit your needs better.

I did not use either one for phone calls and cannot comment on how their microphones are.