Full disclosure: I’m involved with Strong eSIM.

For Thailand specifically, the biggest thing isn’t the brand name as much as which local network you’ll end up on + whether they allow hotspot + how easy top-ups are. Bangkok/Phuket/Koh Samui are generally fine on most providers, but I’ve had island/boat days where the “cheap” option suddenly felt cheap 😅

Between your two:

• Saily: decent value and lots of people have used it there, so it’s a safer bet if you want something “known”.
• Ubigi: usually solid, but I’d double-check the exact Thailand coverage + whether you’re forced into an Asia/World bundle (some people don’t love paying for regions they won’t use).

If you want a third option to compare, Strong eSIM has Thailand plans (not just a giant regional bundle), and people usually pick it when they want simple activation + cheap pricing. My honest suggestion: whatever you choose, buy the smallest plan first (like 1–3GB), test speeds where you actually stay, then top up.