Well I guess I should detail my most recent build. It's a 2002 Bianchi Axis frame and fork that I bought as a complete bike and swapped pretty much everything to what it is now. The drivetrain is a Shimano 1x9 with barend shifter, 42T crank, Shimano XT Shadow rear derailleur, and a SRAM 11-34 cassette.
I chose to run a 1x9 because of its simplicity and also because I haven't seen anyone else riding around here with a 1x9, so I thought it would be cool.
I cut the right side of the handlebars to make the barend pivot point flush with the end of the left side of the handlebar. It makes the bike feel regular instead of having the shifter sticking too far back toward me and my knees. I am running the standard Tektro R200A brake levers which I really like because I run Campy on my roadbike. The crankset is an FSA Gossamer with a 42T non-ramped chainring with a BBG bashguard and a Third-eye chainwatcher on the inside.
The Tektro Oryx canti's are fine and I use the Kool-Stop Mountain brake pads which are excellent! I have no squeaks or shudder.
The wheels are a mix of Ultegra/105 hubs and Mavic OpenPro and CXP?? rims. I had them laying around and they work fine for what I do. The tires are Ritchey SpeedMax Pro's in 700x32c which works out well for my blend of road and dirt rides. I can't attest for their performance in mud or anything. But they are reasonably priced at Performance Bike, so I use them.
I am really impressed with the rear derailleur. The latest XT (and others) derailleurs use a more direct cable routing which is perfect for mountain or cross bike where the cable comes down the seatstay. You can see in the picture below how much straighter the cable run is compared to a standard road bike setup. I think that this evens out the extra friction I introduced in the cable run by running the shifter cable all the way to the stem instead of the more traditional barend cable routing. I routed it that way for 2 reasons: 1. to reduce the chances of getting caught on something/somebody when I fall; 2. it looks cleaner.
Also, the derailleur hugs the cassette more than normal. Shimano calls this "Shadow" and says that keeping the derailleur tight in with the bike will reduce the risk of damage if you drop your bike on that side because now the skewer is the farthest point out on the bike, so it should land on that instead of the derailleur.
With the 42T front and 11-34 rear, I have plenty of gearing for both on and offroad riding. I can keep up with my friends on the roads as long as there aren't any long, fast decents where they keep pedaling after I run out of gearing.