I used TST for years until I switched to Sidebery, and I must say it somehow has all important settings from TST (which I supposed to be impossible - TST caters to tweakers in an extreme way) but is also faster (both startup time and day to day) and seem to use less memory as well.
Some things are in unexpected places (for example I expected to reopen a closed tab with right click outside an open tab - reopen closed tab, but it's in the trash icon at the bottom), but I think they are in better places. Sidebery is better designed.
Sidebery can also save your tabs automatically, something I used another extension for (Tab Extension Manager, which loads very slowly)
I also switched from TST a while ago. I agree with the others that Sidebery feels a good bit more polished.
It also has quite a few more features, like panels for bookmarks and closed tabs and, most importantly for me, integrated tab groups.
But if you just want "less buggy and prettier TST", you can probably just turn all the other stuff off, it's pretty customizable.
I switched from TST to Sideberry, I'm much happier now.
It's still weirdly slow, it somehow takes thousands of milliseconds (entire seconds!) to display the tab list on startup, but much less buggy than TST.
I also switched over a year or so ago and find it a significant improvement with one notable exception: in TST when you hover over a collapsed tab group it would show you a list of all tabs in the group while Sidebery doesn't. Similarly when closing a group Sidebery doesn't show all of the tabs that would close, just the total count.
I submitted a feature request a year ago but got no traction, and now I just expand and re-close groups before mass closing to double check if I need anything.
