Mikely:
Definitely go with Trim-Tex vinyl corner bead (or competitor's equivalent).
The best way to attach it in 4 foot or shorter strips is to simply mix in some white wood glue into your mud. The glue will make the mud stickier and dry harder so that it better supports the corner bead.
What I do is fit the corner bead in place and mark the lines on each side of the corner in pencil. Then I mix up my sticky mud by adding white wood glue to my mixing water, and then using that solution to mix my powder. I apply the mud to the drywall corner first, then to the inside of the vinyl corner bead.
Then I stick the two together and press the vinyl corner bead onto the corner hard with a 3 inch wide knife so that the excess joint compound comes squeezing out the holes. I then collect the excess using the 3 inch knife, wipe the corner bead down with a damp sponge, and put several strips of painter's masking tape across the corner bead to hold it tight to the corner while the sticky mud sets up.
Allow to dry overnight, pull the painter's masking tape off and then mud the corner bead normally.
Vinyl corner bead has the inherant advantage that if it's knocked loose by an impact, you can pull the corner bead away from the corner a little, use a small brush to slip some white wood glue under it and glue it back on. Metal corner bead has multiple disadvantages:
1. If you hit it hard enough to knock it loose, then you've dented it, and you simply can't straighten bent metal corner bead. You have to replace the bent section at least. By contrast, vinyl corner bead snaps back to it's original shape so you can normally simply glue it back on.
2. It's very difficult to remove only a piece of metal corner bead because it's so thin that it's hard to cut through with a fine tooth hack saw blade without the teeth catching on the metal and pulling more of it loose from the corner. By contrast, it's relatively easy to cut through vinyl corner bead to replace a bit of it should you ever need to.
3. Metal corner bead in a damp area (such as on window returns) will rust and discolour the joint compound. Vinyl corner bead don't rust.
I've had experience with both metal and vinyl corner bead, and I'll never use metal again.
From the first link in Cork-guy's list:
"Most pros advise against plastic corner bead due to its propensity to crack or break at some point during installation or maybe in the future."
The above is total crap. The guy writing this has absolutely no experience with vinyl corner bead. It doesn't crack unless you're installing it in -40 degree weather and it's very very cold. It will bend before it cracks but it snaps back to it's original shape, rather than being dented like metal corner bead. Anyone that says vinyl corner bead has a propensity to crack during installation (or afterward) simply has no experience installing it. I have vinyl corner bead around all 66 windows in my building, and I wouldn't use anything else.
"Metal lasts virtually forever and is easier to install. Knowing how to install corner bead properly not only adds a crisp, clean edge to outside wall corners, it also adds protection against this relatively vulnerable area of your home's construction. This area tends to be like the nose on a face: Since it's out there, exposed, the tendency for it to be battered when moving furniture, banged against with toys, or sometimes simply run into from a miscalculation when negotiating a turn, is great."
Which is exactly why you want to have a corner bead that snaps back into shape after it gets a hit. With metal corner bead, if you hit it, it can dent or break loose from the drywall corner, and then you can no longer fix it, you have to replace the damaged metal corner bead. You can glue vinyl corner bead back on.
http://www.trim-tex.com
The above stuff is what I use. I stick it on by mixing white wood glue into my mud to make it stickier, stronger and harder. And, in 66 windows over the course of an average of 10 years or so, I have never had any trouble with the vinyl corner beads. I had more than my share of problems with metal corner bead either denting or rusting and having to be replaced, so I replaced all the metal corner beads with vinyl.