It's down to personal preference I think. Both apps are a cut above any of the Lemmy only apps.

But I didn't like Reddit Sync, so the Lemmy version was still a no for me.

Boost is Boost. It feels like home, and doesn't cost an asinine amount of money to support.

I might be biased because I used Boost for Reddit for years.

I found the customisation of Sync to be severely lacking. The default text size is illegible and the sleuth of options to increase that size have practically no fidelity so end up making the design look terrible.