YMMV but Delicious wins, Foxmarks comes second, Ma.gnolia third and Google bookmarks gets lapped several times before retiring from the race. Foxmarks? Not in the title above, I know, and it’s not an online bookmarking tool like the others, I know that too. But it’s good and worth a mention.
Why do I rate Google bookmarks so low? Well simply because Google released Chrome without support for Google Bookmarks. This is bad because in my view Chrome handles bookmarks appallingly, and given Chrome’s online app focus, a strong Google Bookmarks would have fixed Chrome’s shortcomings. Bad timing I reckon. Ivan’s blog also makes the point that Google has so many apps in development that their online bookmarks offer is bound to get neglected (compared with Delicious). Everything Google has is ‘Beta’, even Gmail. Yeah, right.
Ma.gnolia is the new kid on the block. Very pretty interface. Does pretty much what Delicious does, but I agree with these guys and PARAgiraffe for the moment.
Foxmarks now. This has got very good since they introduced favicon support. It was good before, but I reckon it’s got much better with favicon sync. Before Foxmarks I used Torisugari’s Bookmarks synchronizer, back in the day. But I switched to Foxmarks when Torisugari slowed down on updates. I rely on favicons in my bookmarks toolbar to find my most used links. I can click and go. Here’s a screenshot which I hope will show you what I mean:

Delicious wins for me mainly because it’s simple and effective. Also as Ivan’s blog mentions, it has a healthy business focus: it’s the only thing they do, so they’re committed. Another point in favour of Delicious is that our partners in local schools here in Singapore are using it. There’s also an excellent Delicious Firefox addon. The only gripe I have about this addon is that it takes up quite a lot of space on my NT profile at work – I had to delete this addon since Firefox 3 came out because I couldn’t log out: my profile was too big.
I’ve started a revolutionary move away from IE6 towards using Firefox at our school, but if our IT infrastructure won’t handle the Delicious Firefox addon we might have to do without it. I reckon we’ll manage ok. Here’s what ours looks like so far:

Apart from showing our teachers how great Firefox is, I’m also going to have to persuade them to start using Delicious in their teaching practice. I’m not sure these people know how to make the most of their bookmarks anyway, but that’s another story.
Innova Junior College seem to have the right idea though:
On the subject of how bad Internet Explorer 6 is… check out IE Death March just for fun.