which belt types are good for 3d printing?

[truly_bent]

I know most printers use GT2 belts but some 3d printers like Solidoodle come with MXL belts and pulleys.
Is one better than the other and is there a reason to switch?

Found this pdf on timing belts, which seems to have everything you could ever want to know about timing belt profiles. It certainly has more than i ever wanted to know. Grabbed this excerpt:

"- On drives using a low installation tension, small pulleys, and light loads, the backlash of the GT system will be slightly better than the trapezoidal (MXL) timing belt system. However, with increased tension and/or loads and/or pulley sizes, the performance of the GT system becomes significantly better than the trapezoidal timing belt system.
- The GT system is an extension of the HTD system with greater load-carrying capacity. HTD was developed for high torque drive applications, but is not acceptable for most precision indexing or registration applications. The HTD design requires substantial belt tooth to pulley groove clearance (backlash) to perform.
- As smaller diameter pulleys are used, the clearance required to operate properly is increased. HTD drive clearance, using small diameter pulleys, is approximately four times greater than an equivalent GT timing belt drive.
- The GT system's deep tooth design increases the contact area which provides improved resistance to ratcheting. The modified curvilinear teeth enter and exit the pulley grooves cleanly, resulting in reduced vibration. This tooth profile design results in parallel contact with the groove and eliminates stress concentrations and tooth deformation under load. The GT design improves registration characteristics and maintains high torque carrying capability."

Sounds like there are advantages to the GT design, not the least of which is reduced vibration.