Stihl carb with single screw adjustment

Make sure it is a three screw carb. One screw idle speed, one screw idle mixture, and one screw for high-speed mixture. Many of the consumer saws do not have a high-speed adjustment screw. And if they Have fixed high speed jet they are likely going to be lean and you can't do any modifications because of already being too lean

Do not go with a single screw carb. You will have no control for the high (most important) side. You want a WT 427,590,195 or a WT155 as all of these are fully adjustable. Depending on the top of yours is which one you need. I think your top will change with any of these carbs. My 026 had a single screw carb and it was a little lean for my liking. You can not do a muffler mod on one either (all of my saws have a muffler mod), but I like free power.

WT194 is a popular option as well. Cheapest new price on eBay seems to be about $40 shipped.

I prefer the adjustable carbs too, but I don't have a lot of experience using the non-adjustable versions so maybe my opinion on that matter isn't worth much. Of course, as Fifelaker points out, you might not have a choice if the motor or exhaust has been modified, since the single-screw version is tuned for a stock saw.