It also has been around for alot longer, so its easier to find workers who know how to tune a carb (or say they know). It doesn't mean its better or worse, it just means its a technology that bike builders know. They don't need to learn how to use those new fangled computers. Also, since most customs are purely for asthetics, not really performance, there are alot of people who think a nice big chrome carberator is "pretty".
I wouldn't base your decision on what custom builders do. They aren't building bikes that are truly ment to be riden for as long distances as mass produced bikes, like Harley's, are. I can count on one hand how many customs I've seen that have been ridden longer then 5000 miles. Its all about style, not comfort, ridability, performance (in most cases), or longevity. Do you really think a stretched out bike, with a bandaid for a seat, is really that comfortable?
EFI's are obviously computer based, so they are more effecient then carberators giving better gas milage etc. They can also be tuned alot more procisely, making for a better performing engine (if tuned properly). They also can adapt to changing conditions (i.e. air temp and altitude), riching/leaning the fuel mixture as needed on the fly while a carberator would have to be manually adjusted for those types of changes. Anyone who's gone from sea level to a couple thousand feet up a mountain on a carberated bike knows this all too well.
EFI's you tune it once and forget about it. Carb's, however, need to be tuned every couple hundred/thousand miles to keep them performing at their peak. Annoying in my opinion.
In alot of ways its a matter of preference if you want an EFI or Carb bike. I personally prefer EFI's.
