I started with the popular 229-LF DESIGN marker. They had a great firm-yet-flexible bullet tip that felt like a soft pencil, at times. While they were great, they were a bit short and hard to hold in a pencil-grip, they smelled horrible (xylene solvent for quick drying- ick!), and are now unavailable. On top of all this, about half of the old Design Markers would get pushed into the neck, like a turtle's head, from pressure. Other times, the tip would break off or wear down to a fuzzy nib.
I've also tried the Chartpak AD markers. They also dried quickly and had a long-life, but the tip rotated in the marker when I applied pressure, and I don't always have a very soft hand while drawing- I like to vary the line weight quite a bit, and this became difficult. It is also difficult to get a fine or thin line out of them.
Copic makes a great brush-tip/chisel-tip marker that is refillable. I can't say enough good things about Copic- they are amazing markers, have replaceable tips that are suited for all types of drawing, they are refillable, and the ink is dense and wonderful. The only problem is that they tend to slow down the live caricaturist, as they require a bit more finess and maintenance. Put simply, one must slow down to get the quality out of these markers. When slammed with a crowd in a retail environment, it's tough to speed through and make a good paycheck. That being said, I used Copics exclusively for over a year and didn't regret it a bit. I'm actually thinking of getting a full set of colors, as they're great for illustration.
There are many other sorts of markers- Sharpies, Faber-Castell PITT pens, Tombo brush-pens, Zebra brush-pens, Staedtler-Mars Graphic 3000 brush-pens and others. I can't stand Sharpies, but often use these other tools for different projects and in my sketchbook. Either way, the marker that I prefer now, for live work is the Dixon Markette.
Manufactured in Canada, it seems to be almost identical a marker to the old 229-LF DESIGN marker, save a few points:
1. It doesn't STINK as much
2. It's longer- fits in your hand better
3. It lasts longer
4. The tip lasts longer than the ink
5. It's actually being MANUFACTURED
The Dixon Markette is quick to use, it's forgiving, you can get a sharp, pen-like line and a dark, WIDE brush-like stroke. The tip doesn't deteriorate, and you can draw much faster and cleaner than with a brush-style pen. (I know many artists that can handle brush-pens well, but you're limited to a certain flair or style, whereas I personally see more versatility in the bullet-tip)
I'm not certain where the most accessible or cheap way to acquire the Markette is found, I do know that Kaman's Art Shoppes (the leading caricature and theme park art concession company in the world) uses them almost exclusively. At the behest of the NCN, the wonderful people at ART SYSTEMS did some hefty work and got access to them. You can order them by calling the store at ArtSystemsFL.com and asking for Deidre Harris (or anyone else willing to help). You will have to pay shipping, but they offer a great price. Last I checked, they're nearly $3/marker.