I'm thinking of getting a 9mm BarSto after market barrel for my Sig 226 40cal and was wondering how they work. Anyone here have experience with BarSto barrels?
Any other after market barrels that are good quality?

Bar-Sto makes very good pistol barrels. I have used them on several handgun build ups. Charles the Gunsmith.  

I know many shooters who have them & are very happy with them. I wouldn't hesitate in using them.

I wouldn't hesitate to use them if they make USPc 9mm barrels.

They are some of the best match barrels you can get.  You can get a semi-drop-in or non-drop-in.  The non-drop in will have to be fitted to your gun, the semi-drop in is usually less accurate but won't need much fitting if any at all.  Both are match barrels.
There are other good match barrel makers.

Jarvis and Kart come to mind, both are match barrels.

Stay away from Federal Ordnance barrels.

BarSto is a Tier 1 barrel maker.  Very, very, very good stuff.

Haven't tried their drop in barrels, but just know that in the aftermarket gun parts business, "drop in" usually means you "drop in" at your gunsmith to give him the pistol and parts.  

Im talking about a conversion 40 cal to 9mm barrel not match
they have semi drop in and match
does this mean both need to be fitted?
and whats the difference?

www.barsto.com/category_main.cfm?ID=226&cco=66

Both will need to be fitted. The match version will take more time and effort. Charles the Gunsmith.  

Are there any barrels that dont need to be fitted?
What has to be done so they fit?

Quoted: Are there any barrels that dont need to be fitted? What has to be done so they fit?

If a barrel is loose enough to not need fitting, then it won't be accurate for shit, IMO. As for what's done, slight removal of steel from the lugs on top of the barrel & around the bushing is usually where fitting is done. Charles can answer this better than I can, IMO.

Both the drop in Bar-Sto barrels I have worked fine without any fitting and are pretty accurate, but I know that they are not as accurate as a fitted barrel, no doubt.

I think the chances are fair that a drop in Bar-Sto barrel you get will work fine without fitting.  If you are not interested in top accuracy, just get one of those.  However, Bar-Sto barrels are not cheap because they are premium match barrels and for some people it would be a shame to spend that many clams and not reap the full potential of such a barrel, especially for a fine accurate pistol like a Sig.  The drop in barrels I got weren't replacements for accuracy, I got them to cut down and thread for suppressor use and I don't abide crappy barrels in any case.

Any good smith or perhaps yourself can do the work on a drop in.  As said, you just have to fit the lugs and barrel to the slide.  I would feel confident filing the lug but I would want to stick the barrel on a lathe to reduce the diameter to the point it fits the muzzle end of the slide well.

The non-drop in will be oversized on purpose so that it may be perfectly matched to the firearm.

I'd say if you don't mind the cost and don't want any hassle, get the drop in and with a little luck it should be fine.  If you want to wring the maximum accuracy potential out of your Sig, get the non drop in and let a good smith mate it to your Sig.

Bar-Sto barrels are stainless steel so you may even want to get it finished in something dark depending on your wants.