With regards to my front brake, I've got a few different calipers to choose from. I've already installed a well-used Shimano 600 dual-pivot job, but it seems kinda clunky. I also have a brand new Promax dual-pivot caliper which seems pretty nice, and I've got an older Campagnolo Veloce single-pivot caliper I can throw on.

(My bike is an '86/'87 Bianchi Strada LX with Shimano 600 cranks and pedals, IRO hubs and Mavic MA3 rims, a Velo saddle and generic seat post, a Zoom stem and generic bars, and a Cane Creek "accessory" lever. The frame is blue, the wheels, cranks, and pedals are silver, and the bars, stem, seat, and seat post are black.)

Here are my concerns -- the Shimano 600 is one of my favorite brands/lines of bike parts, period. But it's old and some parts are rusty, and it doesn't "match" as well as the Promax. Speaking of, the Promax is brand spanking new and seems nice, but I don't know much about Promax as a brand (it seems to be a part of Leechi, which I have traditionally associated with cheap stuff.) On the other hand, Campy is a brand that can be trusted, but the older Veloce caliper I have is single-pivot and has no QR level.

Given that, if you were putting this bike together, which would you choose?

given that I don't care about looks i would probably go with the promax since it will probably work best. I did however use a slightly rusty 600 dual pivot for a while and it worked nicely. The single pivot campy would probably be my last choice.

Keep in mind that the brake pads will probably have more of an effect on stopping power. If you can fit nice new pads on the campy it will probably stop better then any of the others with cheapo pads. Of course if they all had nice new pads the promax would probably stop best so...

Same, single pivot campy would be last choice.
Pads are very important
Set up with centering and pad alignment makes a world of difference.

Please note that (if it is the same single pivot veloce I am thinking of) you might have problems getting the brake caliper to center. See if the housing stop is directly over the cable clamp, if it is not, and you try to route the housing aero style, the housing will influence the caliper centering in a most annoying way.

I have a ProMax dual pivot on the front of my Milwaukee. It was fairly weak feeling until I installed a set of the Koolstop Dura holders:



Mine came with the dual compound pads installed so looks similar to this:



It also came with a set of the Salmon pads, which normally would be my preference, but these dual compound ones work so well I have not been tempted to put the Salmon ones on.

These holders and pads transformed the ProMax caliper into something that stops as well as any rim brakes I have ever used. Highly recommended, although pricey.

Promax pads are universally pieces of ****. V-brakes or the ones standard on tektro dual pivot. They eat up your rim, make rhaspy sounds and provide poor braking. The brake calipers are fine, just the stock pads are really, really garbage.

I cannot emphasize garbage enough.

*blink, blink*

What are you trying to say? Don't beat around the bush, here, just tell me what's on your mind.