I've tried several over the years. My first, and still the favourite, is a Joseph Marples like this one from Toolnut -
http://www.toolnut.co.uk/products/measu ... Knife.html - that I bought from Alan Holtam's Old Stores Turnery near Nantwich a long time ago. It's robust, so it'll do delicate and it'll do lean on it when you want a deep trench for a chisel start. The steel is tough enough that the point never breaks off, but hard enough to take a lasting edge, and it sharpens easily. It does about 90% of my marking knife work. For the odd occasions when it won't get into somewhere tight, a scalpel has always done me.
Spear point knives are very fashionable these days, I think on the grounds that you can transfer dovetail marks from tail to pin board on both sides of each tail. Fair comment, but that's only a small proportion of marking knife work, generally (unless you make nothing but dovetailed boxes), and that's only for through dovetails anyway. Falling victim to fashion, I bought a Faithfull spear point knife last year (I'm far too tight to pay the thick end of £50 for a Blue Spruce one) - it costs a few pennies more than the Marples. It seems OK, though it's a bit too thick to get between really close dovetails. It's nice and light, comfortable in the hand, and does everything else well enough.
I have a couple of Japanese knives from Axminster. As you'd expect, they hold their edge very well, though I find them too thin to hold comfortably (much prefer the wooden handles of the Marples and Faithfull), even with a draughting tape 'handle', and since I've already got knives that work, I haven't invested the time to make wooden handles for them.
Almost anything can be made to serve - pocket knife, chisel end, whatever. I think Paul Sellers has demonstrated making one from a redundant small kitchen knife. Should do the job perfectly well.
