Use quark, trust me... currently Torque Constructor is very unstable in the since of .dif making.
quark looks uber/over confusing.
but its much easier to use
(and less laggy, you also dont have to close it to run blockland)
Actually, from my experience of using all programs, here is what I got.
Quark:
Works well and gets the job done, many different options also.
those many dif options make it confusing though, and it is not as easy to add textures.
Torque Constructor:
Well, really great program, got nothing against it.
Hammer.
Also really great, kinda takes long to get it to export a .dif though, and wouldn't be able to add much things to your torque map such as lights,
(The only lighting and such it offers are for the Source engine games.)
If you are a beginner I would definitely advice Torque Constructor.