Started out with Sketchup. Got frustrated when even the easiest things took multiple steps and opened too many holes in the solid, unpredictably. Things like using the 'follow me' just to do chamfers or fillets.
Downloaded Alibre, but read a few horror stories about support and pushy sales (including here) and wasn't sure I'd be willing to pay the $200, so actually haven't installed it yet.
Muddled thru a few parts with FreeCAD. Bugs out regularly, find it horribly clunky overall. All the features, no coherence. BUT that said it does tend to make a nice model eventually, and is still my go-to for final steps after exporting STLs from elsewhere (see below).
Recently found Creo Elements myself from a pretty good listing
(which I can't link now as a new poster. do a websearch on 'craftsmanspace free 3d cad' and it should show up)
also recognized it from a post of Ian's (been reading here before I registered) and downloaded it, and think I'm in love. Free? Amazing...and totally eliminates any urge to pay for (or even try at this point) Alibre. The only thing it seems I can't figure out how to do that I wish I could is the 3D text as someone else mentioned, and it will Export but will not Import STL. But it does surface blending, varying-radius chamfers and fillets, all very smoothly and easily.
So, I think my 'real' part designs will be done in Creo now - features remain easily editable for tweaks after prototype printing and the like, has some nice clash analysis for multipart assemblies that need to be glued after printing. Hold on to Sketchup for outputting 3D text STLs, and use FreeCAD to import and unite the two if I want text embossing on the part. (Plus I find Creo's coordinate system "origin" a little hard to figure out since everything is working planes - seems to be the origin of the first working plane w1...but I tend to delete working planes to keep the clutter down as I make parts. Just as easy to push the STL over to FreeCAD briefly, reorient if necessary, and re-output. Then again, I confess to using Repetier's bedding to do the same: import 2-3 STLs, place and rotate how I need to, then slide them all over to "off the bed" around the (0,0) origin to resave and then do actual slicing/printing in Skeinforge/Pronterface.