Metal or Carbon Resistors - Which is better?

I know you are trying to minimize coloration by utilizing a passive linestage, but, ultimately, the goal is to achieve the best sound by assembling good and compatible components.  The challenge with passive linestages is a loss of dynamics—the sound tends to be less lively than that of good active linestages.  To me, this would be particularly of concern with 300B amps which also tend toward the polite and undynamic side as compared to 2a3 and 45 tube amps.  
 

I would not narrow the field to any particular design or approach.  While I’ve heard some good passive systems, in most cases, I’ve preferred a good tube active in direct comparison even when the system was theoretically passive compatible.  The active system tends to be more dynamic, harmonically rich and saturated and more engaging—are some of these qualities ‘colorations”?  Perhaps, but who cares?

@larryi 

Appreciate the thoughtful take and advice. I wouldn’t be here if I didn’t keep an open mind :-) 

Metal better for audio applications. Look it up. 

I too would be wary of using a passive pre with 300B. As for 300B lack of dynamics, depends on power supply and speakers used with, I have absolutely no issues with my monoblocks, each has equivalent power supply to what I see in many stereo 300B. And I've directly compared my 300B amps to my 845 SET from Coincident and Art Audio. 

As for the pre, Coincident Statement pre DHT with dual TVS  I'm running with all factory upgrades and some of my own provides all the transparency, dynamics, voicing, presentation I could ask for. This more sympatico combo than a Pass XP22 I previously owned. Latest Coincident pre runs 300B's vs the 101D's mine runs. Vinnie Rossi also has a very nice 300B I considered. DHT pre's are excellent matches for SET amps.

Most vintage gear used carbon film, as they were much cheaper over metal film. Then there are carbon comp resistors that are garbage. We're talking about 1/4 and 1/2w that are the majority in all our gear. The 5w and 10w ceramic resistors are a different story.

Almost all new stuff uses metal film as they are basically the same price as carbon now.

carbon film have much more noise over metal, but are a little more warm sounding. In the signal path, metal should be used, most important in high gain, as in a Phono-pre. In the power supply, and other places, carbon are fine to use. Anytime i replace a resistor, it is with metal film. 

Are there even better ones? Of course. But they can get stupid expensive. They really only make since in things like crossovers.