fishermans hands down, use at least a double but i would go a triple (pack and pre-stress it properly) - you will never want to untie it anyway...
a double fishermans will NOT undo easily once you load it up a lot. but then again thats a good thing! it has excellent cyclic, static, and dynamic load properties, as well as always dressing itself correctly. If you put a stopper on it by tying an overhand knot around the line then it is all but failsafe, as well as being very compact.
Rethreaded Figure Eight is actually "Better" because you can untie it more easily (a little bit at least), but it is a chunkier knot and is significantly weakened if you do not "pack" or "dress" it correctly.
i doubt you will undo a blood knot once it loads up properly if you use anything other than fishing line - plus it's a "messy" knot
a water knot is better (stronger) for tapes & webbing rather than rope, string or line. plus its not great with cyclic loading and can "undo" itself.
The Albright Knot is a death knot - dont use it on anything you need to stay tied.
see
caves.org/section/vertical/nh/50/knotrope.html for one comparison or knots with static and dynamic loads.
wach out though as you have created a nice snag point for your other lines... I would either shorten the lines or buy new ones and keep these as spares.
is it possible i am more paranoid than silviu?????