The best finish for anything usually boils down to opinion and what trade offs are important to the individual. Every finish has strengths and weaknesses. This is a vast subject, and anything anyone has to add is only scratching the surface, but here are a couple of my own opinions and what I tend to do these days.
Chrome: I have chrome done regularly. It is extremely difficult to get done well, and dreadfully expensive. As a rule, I limit my chrome parts to hardware like shifter and brake pedals, small things made from steel. Chrome itself is microscopically thin to the point of transparency, but it is wondrously corrosion resistant. It is a thin layer on top of nickel, which is very tough. The nickel is on top of copper which serves as the bodywork to smooth out your part. A complete frame is an insane amount of work to make smooth and defect free enough to look good chromed, but it can be done. I have a high bar, and my parts are already flawlessly smoothed and mirror polished before I send them to chrome and it is major work and still expensive, but many parts are ok on the first pass. Large parts in general are just not an option for me, I can't imagine doing it unless I built the frame from scratch and it was already pretty enough to chrome. Preparing a manufactured frame? No way for me.
I almost always paint my frames gloss black. With single stage polyurethane over epoxy. Even with paint, it is a lot of work smoothing out a production frame so it looks good in shiny black. Dozens of hours if you are picky. Most frames do not look good in a color no matter how much you fuss over them if there are a lot of stamped components. The manufacturers go to a lot of trouble to cover or camouflage their frames and paint them satin black for a reason.
In the main I paint most important parts such as hubs and brackets just like the frames for durability, and because I can control the process from start to finish.
I have nothing at all against powder coating, but seldom use it. This is mostly because I am already doing parts with urethane, and the superior toughness of the powder usually is not needed enough to send parts out. I am as a rule more concerned with longevity and corrosion problems, and powder coating offers no advantage. (No doubt others will disagree, but there is only one way to solve aluminum alloy corrosion issues and that is to chemically passivate the parts which is dangerous (and illegal), though it works as well under powder as it does under paint).
Powder is tougher and more chip resistant, but it does take damage. I can't say it is much different to "repair" than urethane - touching up damage usually looks touched up regardless. Maybe you can't cook your powder touch ups, but you can certainly just use matching paint to make a repair. I remember a dragster chassis done in a pewter hammer finish powder, and it was shit where it got chipped, but can't say paint would have been better except for probably actually having paint to touch up with. Having that perfect match powder doesn't help much as far as I know. I have never seen "spot" powder done.
