+1 for leave it untied and use flat overhand if you need a loop - back it up.

I usually leave the ends untied because I find that less then half of what i use my cord for is anchor building, and of that percentage a lot of the times I will make an equalette instead of pre-equalized anchor. i find it just saves time to not have to untie a knot every time I want to use it, but I guess it boils down to intended use and personal preference.

Rarely carry one, but when I do:

Double fisherman's in 7mm perlon.

I have a retardedly long 26 foot cordolette I keep permatied with a triple fishermans. I have used that method for 12 years and have yet to need anything longer that required me to untie it. If I need shorter just clove hith the excess out of the way.

If you know 3 usable knots to tie a cordelette with why do you feel the need to ask redundant questions on mp and waste forum space? Using the rope as your anchor is bomb (and should be adopted by most climbers in my opinion... ) A patagonia knot; Overhand knot on a bite with a backup Knot is an quick and easy one to tie and untie giving you the freedom to use the full length of the cord in a pinch (a situation that the only bomber gear you can get is very spread out and a looped 20ft cord won't cut it.)

Also welded knots (ones you never untie) are considerably weaker than newly tied ones. This has been the cause of many climbing related deaths.

Always carry one twisted and clipped on th back of my harness. Figure eight I believe Flemish finish on both sides

Usually anchor with the rope at the Gunks. (double ropes, actually)

But, when I do use a cord it's 7mm perlon with a double fisherman's.

I try to keep the legs equal length since the shortest leg will see higher load. When I need to extend a leg, I use a less stretchy Dyneema sling instead of untying my cord and using only one strand.