Carburetion options

Choosing what kind of carburetor that is best for your bike is quite the controversial subject, but when discussing it with other biker or mechanics it all boils down to one thing... Opinion, and opinions are just like assholes - everybody's got one, and yours usually stinks!

The best way that I can recommend choosing a carb is to stick to carburetors made for your bike.
Yes, those Dellortos and SU carbs look cool but they were actually made for sports cars and modifying them to work on motorcycles can be extensive and expensive.
All I can do is give you my own opinions based on observations from decades of working with these products.

Bendix (Zenith)
Keihin Butterfly
Keihin CV 
RevTech
Holly
Edlebrock (Quicksilver)
Mikuni
S&S

Bendix (Zenith)

I get a lot of the ole-timers that are committed to the Bendix (Bought out and now owned by Zenith) Carb but the simple truth is that the there is no way to regulate the accelerator pump to work properly and the throttle shaft seems to wear prematurely. If you get it to quit coughing out the air cleaner you will be fouling plugs. The only thing that I have found going for those carbs is that they are cheap (but then you get what you pay for). The ole-timers will swear what a great Carb the Bendix was, and the truth is that when the Bendix first appeared on a Harley it was a great carb, but greatness was not hard to achieve considering that before the Bendix was the Tillotson (two steps up from the original tomato can and wick). If you have a Bendix, the best advice I can give you is to stay away from the adjustable main jet. If yours has one, convert it back to using regular jets and go back to tuning it the old fashion way, change a jet, ride, read the plugs, repeat. It's more of a pain in the ass but at least it should stay set the same from day to day.

Keihin Butterfly

The Keihin "butterfly style" is also a good carb and can be tuned easily and accurately, but similar to the Bendix it is plagued with pump problems and sucking air through the throttle shaft area.

Keihin CV

The Keihin CV (constant velocity, also known as a vacuum slide) that comes stock on the later models is actually a very good carb. It is a bit of a trade off, you give up a little performance for a little better fuel economy, but it is a very reliable and dependable carb and it is not that hard to adapt to earlier model bikes with only a few modifications. Many riders can't get used to the hesitant throttle response, but you can make this carb perform incredibly well with a few simple modifications.
Refer to the CV Carburetor Modifications page for a guide to making your stock CV perform like a champ!

RevTech 

I am extremely disappointed with just about every product that comes out of this company. Every customer that I have had install this carb on their bike has returned within a year to ask that it be fixed and every one that comes in my shop ends up in the trash because it's already worn out.

Edlebrock (Quicksilver)

I get a lot of flack from the performance guys about the Edlebrock Quicksilver, something about the fact that it's a "flat slide" carb it's supposed to be the optimum type of carb for a Harley type of motor.
 All I know is that in about '96 or '97, when all the hype about it being the only "American made" carb was going on, I installed a shitload of them and about 85% of them came back and asked to have their old carb reinstalled.
 Why? Maybe bad performance? Nope, they all said it ran great.
 Maybe it trashed there mileage? Nope, it decreased a little but not that noticeably.
 The reason most folks brought them back was because it hurt their wrist! 
The spring on the slide is too stiff and the riders arms were getting tired from holding the throttle open for more than a few minutes on the highway. 
After speaking to company I was left with the impression that their stand on the subject was "Tough... They can suffer, that carburetor works (sells) great". 
The Quicksilver can be tuned to run pretty good if you purchase that neat little adjuster tool that you screw in the top of the carb but it's only for setting the adjustment folks, after you get it set you have to take the tool out and put the plug back in or you will start to suck air through the tool. (It cracks me up every time I see one of those full blown customs in Easyrider with that stupid tool sticking out of the top of the carb)
 

Mikuni

The Mikuni is probably one of the best performance carbs you could put on an H-D whether you are looking for a good street or race carburetor. What nobody tells you is that you have to be a fucking rocket scientist to try to tune the son of a bitch. The damn thing has five jets in it and you almost have to have access to a dyno for an entire day to get it tuned perfectly. There are some guys that are really good at tuning them, but you can bet they've had some dyno time before. I also found that the Pingle Guzzler and over size fuel line couldn't keep the tiny little float bowl filled all the way to the end of the drag strip.

S&S

The S&S Carburetor is the only carb that I will recommend or endorse. I don't have to say a word about it's performance, I'll let the drag racers do that for me. Take a trip to the All Harley Drags sometime and notice what's on 99% of all the drag bikes. It's very easy to tune and is basically a "Set-it and forget-it" application for street bikes. Used with an inline fuel filter it is pretty much maintenance free (clean the fuel and air filters occasionally). It can be used on all Sportsters, the old Flatheads, Knuckles, Pans, Shovels and the Evos and Twincams. Everything from the 883 & 900cc Sporties to the Shovel FLH to the Evo style 145 cubic inch monster motors (why do those guys build them things for the street anyhow?).
 I Put an S&S Super E on my Shovel in '94 and have put around 80,000 miles on the bike since and I have never touched or changed anything on it in ten years, other than the air filter, never needed to. 
The Super E is best for most street bikes, the Super G for the bigger inch motors and the Old B and D models make for great drag racing carbs.
 I installed a Super E on an old '71 1200cc FLH and the only thing the ole geezer didn't like was the fact that when he lets go of the throttle, it snaps back closed. His old throttle never did that (I had to convert him from the old internal throttle in the handlebars to an external set-up).
Refer to the S&S Carburetor Tuning page for a guide to setting and adjusting your S&S Carburetor.

Here is some info about jetting your carburetor.