My experiences with SunRace freewheels have been poor. They have all been loose on their bearings, causing them to clank noticeably during pedaling in some gear combinations. After a few hundred miles, they had damaged their own internals enough to begin chirping and squealing.

Their friction shifting feel was nice, though.

They're both basically Tourney-level, although the HG37 is theoretically probably slightly higher-grade.

Personally, I'd get whichever you prefer as far as tooth counts.