I have tried most of the forms of transmission out there and if you can afford it then get the ball screws or even a good anti backlash lead screw. The anti backlash lead screws are still good value for money and the polyacetal nuts are very good wearing. I have a 12 start leadscrew on my x axis and its great. Fast rapids and pretty good control when geared down about 3:1 on the motor.
A lot of people make their routers very accurate but if you are only cutting wood then it needn't be as wood swells and contracts with moisture in the air. It's only the positional accuracy that you need and not resolution. i.e it has to come back to the same spot all the time (no backlash or looseness in the mechanism).
I went from belts to leadscrews to ball screws over a year or two so it would have been cheaper right from the start to get the ballscrews and have a good machine from the get-go. if you want a machine to last for the next 10 years or so then go ballscrew or anti backlash leadscrew.
Some of the Chinese ballscrews are very cheap but you need a press and lathe (or Vee block with indicator) to straighten them out when you get them as they are like spaghetti and are all over the place. I don't have a preference for either but the leadscrews with polyacetal nuts are better in a dusty environment. I have ballscrews on my Y axis (long) and to keep the dust out I loop a leather bootlace over the screw twice with a 3/4" nut hanging off the bottom of it to add some weight and do this on both sides. It wipes the screw before the nut goes over it and keeps 90% of the crap out of them. I grease the screws and don't oil them. I also have a fairly good dust extraction system which I think for a wood router is absolutely necessary not just for the machinery but for your lungs.
Here in Australia a few years ago the Gov health agency listed ALL Australian hard woods as being carcinogenic. This would probably be the same for a lot of woods in other countries as well. It makes sense to combat this problem at the source and not later through medical situations. Prevention is better... Blah, Blah, Blah, as they say.
Don't get single start leadscrews as the rapid traverse is just not fast enough. It's good for a metal machine for cutting but not a wood router where you need rapid repositioning. Get something in the way of 4 start or 20mm per rev (3/4") and gear down your stepper to about 3:1. I wouldn't go under 10-15mm per rev as it just too slow.
Steppers work stronger and better at low revs and if you have 8-10 microstep drives then the accuracy is as good as you need.
I hope this helps you out somewhat.
If you want toothed belts then the only ones I would recommend are the TDH belts or the ones with the rounded tooth profile as they seem to fit better than the sloped sided ones. (Most photocopiers I pull apart have TDH belts so the manufacturers can't be wrong) I have bought most of the type of belts on the market and the rounded ones definitely fit the best. I only use the belts on fast moving stuff now like a laser head etc that has little mass or weight to push around and I use leadscrew or ballscrew for the rest.
Ultimately it come down to what you can afford but my recommendation is to go with a screw type of setup.
Richard.