[asid61]

Solidworks is pretty amazing. All CAD programs are. I can get a very accurate weight estimate including screws/rivets without too much trouble. I have had problems with motion due to a slow computer though. SW slows down a lot for smaller/older laptops like mine (4gb ram). I tried to load a particularly interesting swerve design from CD and SW crashed due to my slow computer.
I can't speak for Inventor because I;ve only seen it being used a few times, but it looks very similar to SW to me and apparently has a gear generator, which is useful if you don't want to download dozens of models of gears like me. It also has a darker color scheme to my eye.

Keep in mind CAD is almost useless if you don't use materials or dimension properly. I haven't used the stress analysis tool in SW but I plan to start soon. You should have at least one person on your team thouroughly versed in CAD (can use almost any tool in CAD) regardless of what program you go with.