I post here my little styleguide for building tracks.
If it is possible, place the track on the same level as the default terrain. Don't build any tunnels/ridges/dams/bridges if you don't need to. Also the turns should be as fluent as possible and the tracks don't have to be axis-aligned.
If the track is slightly above the default terrain (less than 4 blocks), put it on a dam. A dam should consist of dirt (or other surface material) and should have a 45-degrees slope on both sides. If the dam needs to be too wide, you can make the slope steeper but then you should reinforce it by building a wall. If the track is too high, make a nice bridge instead.
If the track is slightly bellow the default terrain, make a walley. There should be a 45-degree slope on both sides. If you need to subtract too much material to make the slope, make it steeper but reinforce it by building a wall. If there is a naturally-generated cliff next to the track, you can keep it as is. If the track is too deep, build a tunnel instead. A tunnel should be 4 blocks tall. If there is going to be only one-block thick layer above the tunnel, destroy it and make a ridge as described above.
Use digtrons or worldedit only if you are aware of all side-effects. Also keep in mind that such tools usually don't do all the job, you still need to look at the result and fix the issues.