There was an article posted a while back on do's and dont's of car restoration. One of the Dont's listed was drum to disc conversions. Being in the process of one myself at the time, I took exception to this. Everyone is entitled to their opinion, but here is some of my thought process on why I proceeded with mine
The Carology I have absorbed over the years tells me that around 70% of a vehicle's stopping power comes from the front, which is my understanding of why modern cars still tend to have discs on the front and drums in the back. I understand that front drums are bigger than the rear drums on drum-only cars, but I'm not sure how that stacks up with disc brakes for stopping power. Personally, I don't stray too far south of the 70s in my car selections, and prior to my current 65 Impala, I have only owned one other car that (potentially) had front drum brakes. It was a 66 Caprice and it was early on in my car collecting career. This car had a lot of problems, and they were beyond me at the time, so I didn't keep it long and sold it. I don't really recall how the stopping power stacked up to the front disc cars I usually drive, so I can't really speak with authority on stopping power. What I do know from my disc/drum cars is that the adjustment on the drum brakes is a factor in pedal travel and response time - which I imagine gets worse when you are dealing with four of them. I would say personally that stopping power alone is not enough to justify a conversion.
I just plain hate drum brakes
I can swap out a set of disc brakes in about 15 minutes. Drum brakes always turn into an adventure which generally starts with me taking a picture of the brakes so I know how to put them back together again
Fighting with the keepers, springs, park brake lever, freeing and lubricating the seized starwheel... it is always an adventure. This alone is almost enough to get rid of the drums - although I did keep them in the back
Single Circuit vs Dual Circuit
I'm sure there are exceptions, but almost always front drum brakes come with a single circuit brake system. This is extremely dangerous and is reason alone to do the disc brake conversion. About two weeks ago, I popped a brake line in one of my 90s era (dual circuit) vehicles during a brake check in Philly traffic. Not only did my remaining surviving circuit provide me with enough stopping power to avoid a collision, but I was able to limp my stricken vehicle through Philly traffic to home base one state away. Now I know the response to this one is replace all of the brake lines and you'll be fine, but when I went to replace said brake line, I found I was not the first person to perform this repair. This alone is hands-down justification for a conversion
What are you starting with
This is the million dollar question for any mod scenario. If you are LS-swapping an older car with a completely serviceable drivetrain, we are not going to be friends. But if the drivetrain is toast - or missing altogether - different story. In my case, I had a seized single circuit master cylinder, corroded rubber brake lines, a questionable brake booster, seized wheel cylinders, etc. I was investing a few hundred bucks in this brake system no matter what. for a little under a grand, I got 90% of what I needed (I kept the rear drums). For me, this was a no brainer
Unless it is a non-driver, original, halo car of sorts, discs are better.
This coming from a guy who balances the 4-wheel Buick drums like a boss.
You put seat belts in your car, right? Same-same.
I also switched to discs in the front and left the drums in the rear. However, I don't think the answer is totally A or B. Some cases are different, and so should the solutions be different. For instance, a very lightweight car, driven in light traffic at lower speeds on good road surfaces, might do just fine with drum brakes up front. (I know, I know, I certainly didn't just describe Philly traffic, but it could happen elsewhere!) Conversely, a larger, heavier car, driven fast in heavy traffic - well, you get it... And there are plenty of mix-and-match variables that can affect the choice.
In general, drum brakes are lighter than discs (again, there are exceptions) - and if not put under heavy, continuous use, can perform just fine. In fact, many drag racers use drums to save weight (not an absolute, but in a lot of cases). No successful autocrosser, however, would risk all his corner-braking to old-style drums. Aesthetics can also come into play: finned aluminum drum showing through some spoked or slotted mags look tons better that discs. On a car that is just driven on Sunday to the local show 'n' shine at 45 mph, that "look" might be important.
So I'm not making a case for either, really - just sayin' that there are instances where either choice might be the best, based on any number of factors. My car is 4000 lbs. and I drive on some rather curvy roads and sometimes at freeway speeds or in heavy traffic. So I chose discs. But honestly, when I'm constantly wiping that brake dust off my chrome Cragers and washing those black polishing rags, I sometimes secretly wish for my old finned drums up front!