Read thru this current thread
http://www.fishing.net.nz/asp_forums/line-knot-issue_topic107355_page1.html

I've found the J knot to work well for braid to braid, it's the third image here: http://www.fieldandstream.com/photos/gallery/fishing/bass/where-fish/2009/02/strongest-fishing-knots?image=2

I use Improved Albright knots joining braid to leader all the time. It's important to double the braid so it gets a proper grip on the leader (and I have found a tied double is much better than just doubling it and later trimming at the knot).

It's also important to lubricate it with lots of spit and to pull it up really tight, pushing the wrapped braid as far as you can back towards where it came form. I usually go 9 turns up and 8 turns back.

Not only has this secured many horses of snapper on 10lb braid/20 or 30lb fluoro, but we also use it on our 24kg braid/80lb leader kingfish jigging gear.

Lots of practice means I tie the knot very slim and trim it really close, so it slips through rod guides easily. The only failures I have had in the last few years have been where I've trimmed the line in the knot - but that's been maybe twice in the last 3 years.

10lb braid to 10lb braid - I find a blood knot with plenty of turns works as well as anything, though admittedly it's better with the limp rather than fused braids.

Its huge advantage with these light braids is that it ties down very small, so doesn't catch up the rest of the line on eg small baitcaster spools (or line guides), so doesn't hinder casts.