I have mostly only used SR3D Builder, and I really like it. It's simple and the parts align, rotate and snap wonderfully. It's very quick and easy to use. However the only thing missing really is the possibility to use flexible parts such as hoses, strings, chains etc. It's sad that it will (most likely) never be updated/edited...
I'm considering moving over to LDCad, but as I've read some of the posts, some people say the parts doesn't rotate/align as preferred. How easy is the program to work with? And how well does the editing of flexible parts work?