Is there any collection of quality demos from the past year or two? Something that has final matches of the big tournaments, in an easy to download - easy to watch package. Or maybe just a collection of links to download these individually?
And the same for all-time best QW demos?

It's not easy but here is a lot

ChallengeTv torrent

You can get some from the evening cup i hosted a year ago on the tournament page (click the VS link for each game :p). No proper naming of the demos though unfortunately.

EQL 19 final http://eql.quakeworld.nu/eql19/matches/63#Played
http://demos.quakeworld.nu/download.php?id=144

I found this demo archive in my favourites:
http://demos.igmdb.org/LeopolD/QuakeWorld/
Well sorted by event.

EQL Finals with commentary: https://www.youtube.com/user/darff37/videos

I hope to add more demos here: http://fpsplaybackdemos.netne.net/fpsdemos/index.php
and hopefully other people help with that.

Also, this is fun:
http://fpsplaybackdemos.netne.net/demosearch.php