From the GH forums most people seem to think the chery mx black is the worse for a spacebar.
Clears best for spacebar

well that is the general consensus anyway.
ABS plastic is better than the plastic used on say Logitech/Dell etc which uses some other lesser quality plastic. ABS is usually found on old mechanical keyboard casings.
PBT is used on newer mechanical keyboard these days; however they still use abs from time to time because it's cheaper.
Abs will make the keys shiny eventually after hard use. Pbt will have less or no shine with use

Also pbt yellows less compared to abs.
QUOTE
Key Materials and Key Wear
There is a bewildering array of plastics available and when you add in the different additives for softening, the ability to mix plastics, and fire retardants it's not easy to generalize how keys will wear. In addition, keyboard manufacturers generally will not advertise what materials they use in keys and focus instead on cost cutting. These are some of the plastics you may find to be in use:
PS, PC and PVC (Polystyrene, Polycarbonate, Polyvinyl Chloride). Common and cheap. This is a lighter less durable plastic that tends to be vulnerable to solvents. Most keyboards shipping today including Logitech, Microsoft, etc. use some variant of this for their casings and keys.
ABS (Acrylonitrile Butadiene Styrene). It's commonly used for older keyboard casings. It's a comparatively soft material compared to some modern plastics but is resistant to breakage. Topre casings are made of ABS and probably most IBM Model M's are as well. Although I am not sure I suspect Filco and Das keys are made of ABS.
PBT (Polybutylene Terephtalate). PBT is a common choice for modern Cherry keycaps and is what IBM and Unicomp use. It should not yellow as much as ABS over time.
POM (Polyoxymethyleneor better known by the brand name "Delrin"). An abrasion-resistant and low-friction material, this found use in older black Cherry G80 keycaps. However it is expensive and not common in other keyboards.
Read this wiki article to find out more about the differences in the plastic material
http://geekhack.org/showwiki.php?title=All+About+KeysAnyway bottom line is; if it's ABS, PBT or POM it should be fine; and is way better than the normal crappy PS, PC and PVC (Polystyrene, Polycarbonate, Polyvinyl Chloride) used in logitech/microsoft etc keyboards.
This post has been edited by Moogle Stiltzkin: Dec 7 2010, 01:07 PM