I've been using Nova Braid NovaGold http://www.novabraid.com/pdfs/LR-P20102-Novagold.pdf now for about four years. It is amazingly stretchy, high strength, offers very low abrasion, does not hockle and works very well in my windlass.
The Nova Braid NovaGold double braid anchor line offers better elongation than does New England Ropes 3 Strand anchor line and also better elongation than NER Mega Plait.

According to the manufacturers spec sheets, linked below, at a 30% working load the NovaGold double braid will stretch about 14%. At a 30% working load New England Ropes 3 Strand will stretch about 3-4%? (I suspect the spec sheet is off as it should be closer to 10%?) & Sampson 3 strand about 10%. The NovaGold is actually more elastic, flakes better, has better abrasion resistance and does not hockle. It also works very well in my windlass even though I don't use it much. The only draw back I have found thus far is a tough splice to chain.

Even NER Mega Plait, which I used on my old power boat, and really disliked, does not do much better than the NovaGold double braid in either tensile strength or % elongation.

NER publishes a 20% working load stretch for Mega Plait of 10.4%. At a 20% working load. NovaGold double braid offers a 12% stretch and the individual strands don't pull and pucker like Mega Plait can, which is the reason I did not like it.

NovaGold double braid, according to the manufacturers specs linked below, beats both NER 3 strand, Mega Plait, and other anchor rated lines, in tensile strength.

Here are the specs for 5/8" rodes:

NER 3 Strand------------------------------------ 3%?----------12,200
NER Mega Plait - 12 strand -------------------10%-----------10,000
NovaGold DB ------------------------------------12%-----------14,800
Yale Octo Brait - 8 strand ---------------------12%-----------12,200
Sampson 3 Strand ----------------------------- 10%-----------10,000

Links:

NER 3 Strand - http://www.neropes.com/Datasheets/MAR_3S_nylon.pdf

NER Megaplait - http://www.neropes.com/Datasheets/MAR_megaplait.pdf

NovaGold - http://www.novabraid.com/pdfs/LR-P20102-Novagold.pdf

Yale Octo Brait - http://www.yalecordage.com/pleasure-marine-ropes/anchoring-mooring-specialty/nylon-brait.html

Samson 3 Strand - http://www.samsonrope.com/index.cfm?ind=1&app=5&rope=25&inst=1

NovaGold can be purchased from http://www.cajuntrading.ca/ and the price is amazingly affordable, was less than NER 3 Strand.