may I suggest you visit TopSolid web site. (Removed by Mod).
you will find a complete CAD and CAM sytem like PTC, Solidworks is limited to CAD and mainly prismatic shape for free form they need outside software like Rhino witch is good for the money but poor in quality.
also I recommande you look at a solution that is integrated it save you from the deasagreement of version realse of the different product witch is never in sync. 1 cant read the other.
It totally depends on what type of work you are doing... and how complicated/involved it is.
First, it is very dependant on what kind of design engineering you will be doing. Are we talking about single component designing here (couplings/machinery/etc.) or are we talking whole Plants (Refineries, Mills, Mine Process Plants, etc.)
Secondly, it also depends on whether or not you will be doing mainly 3D or 3D work. I will try and summarize below.
If you are only looking at a design engineering software for 2D work and drawings, then I would suggest Autocad for your use.
If you are looking at software for 3D work then it depends on the first factor of what scale projects you are working on. If you are only looking at single component design then I would strongly suggest Solidworks for you. It is a MUCH easier program to use than Autocad, and like I said is very suited for single components. However, if you are looking at designing an entire mill/process plant/ etc... then I would strongly urge you to not use Solidworks. It simply can't handle large projects and like many other engineering firms, you will find that simply cannot perform. For larger projcts I would suggest Autocad and possibly even CADWorx.. which runs through Autocad. I have used Autocad for large engineering projects over the years and it performs quite well.
I hope that helps... but without any details it's hard to suggest a program for you.