MLCad, the LDraw interface that I prefer, is not so quick to use for building and has a steep learning curve for some things (such as LSynth), but I find it more precise when it comes to brick placement, and it supports some clever things such as LSynth and exporting models to POV-Ray files via LDView, and it has a very customisable parts menu. As the parts library is user-created, it will continue to grow, and there is even the ability to convert parts from LDD to the LDraw format, if you know how. The MPD (Multi-Part Dat) format function is also very handy, and I find having actual submodels more useful than using groups.
SR 3D Builder is a good alternative to MLCad, as it has a more LDD-like interface, but I found the positioning a bit clunky (which might just be me), and there is currently no LSynth support (which I am a big fan of). The locking pieces function is great though, and it'd be good to see something like this in MLCad (which has already been proposed). The ability to have working Technic gears and animations is also a great idea.
If you want to use the LDraw parts library, but want something easier to use than MLCad, then SR 3D Builder is probably for you.