Which temperature coefficient for resistors?

[Brett Duggan]

Hi folks,

I need to buy a variety of metal film resistors for use in an ASM-1 along 
with various other synth-DIY projects.  The resistors I wanted to 
purchase come in both 50ppm and 100ppm varieties.  Are there any 
particular reasons why I should choose one kind over the other, or is 
this irrelevant?  Would it be okay to mix both kinds within the same circuit?

Thanks very much for any help,
Brett D