Reference management software, Endnote and others

Hello. I'm starting a PhD in January, but I already have a messy pile of notes and a folder full of URLs and citations, so I'll need to start using a reference manager now, I think.

I've never used one, before. Can anyone recommend one based on their experience?

Endnote seems to be the industry standard, or certainly the biggest name. But I've seen lots of mention of Zotero, Mendeley, Refworks and many others.

I use Firefox and Chrome, and Microsoft Office 365. Features I'd like include the ability to annotate references/attach my own summaries of the reference, and to synchronise across devices (I work between a laptop and a desktop). I strongly prefer a downloadable app, rather than one based only in the cloud. I've had to work offline, at times.

Free is, of course, preferable! Are there any good free ones that don't kill their own useability with ads?

Grateful for any recommendations!

Cheers

P.S. there is a another thread on here about reference managers, but it's over ten years old.