As always, this is just my personal opinion.. and more intended for beginners not higher end people who would be using things like Maya, and professional modeling apps.
1st place - Fusion 360 - By far the best free 3D application out for mechanical modeling. It's REALLY powerful. Solidworks is the pro's choice in the past and many still swear by it but I see more and more people (and more than a few companies recently) switching over to F360. And Solidworks is so out of price range for a normal human to afford as a hobby application F360 is really the best back for the buck (zero bucks actually if just a hobbyist) link to - Fusion 360 free for hobbyist and students
2nd Place - Onshape - Onshape is very close to F360, they both work well, both are cloud based, sorta. Onshape is 100% cloud based where F360 is able to work offline being an independent app so because of that there is no working offline with Onshape. they recently changed their file privacy base also which a LOT of people have issues with as they can't work on something and release it when done because it's always up and publicly accessible.
3rd Place - TinkerCAD - Super simple kinda lego block mentality of building an object. Place blocks or cylinders or what ever and add or subtract items to build up an object. Plenty of tutorials right there on the website. Still about the easiest to do simple modifications to existing STL files. I use it over Fusion as it imports and Exports the STL far faster and easier than any other 3D app I've seen.
4th place- - there are a bunch of odd balls, many are rather powerful but can be confusing for the average user as they use coding instead of a user interface to work in, or have odd issues. search the web if interested in those
Slight off Options - Blender - Blender seems more a organic modeler, but many seem to get it to do amazing mechanical items with it.
FAIL- Sketchup- Ugg For some reason there are still a small group of hold outs using Sketchup. It's actually a decent architectural designer program. But it's poor handling of curves and arches as well as it's beyond glitchy and poor STL export which will make you run files through external apps to clean up makes it rather terrible for 3D printing.
1st Place - Sculptris - Simple, easy actually down right fun to use "push clay around" type of modeling. great for beginners.. SOO much better if you have a pen-tablet setup, don't need an expensive Wacom as the cheaper ones work with it fine (though a Wacom is a nice improvement)
2nd Place - Blender - Blender is an odd one out. It's WICKED powerful in the right hands, but can be really hard to learn. the whole interface is one sided and they want you to work their way, which can be good if you think like them. If you don't then it can be impossible! I highly recommend you at least try it . you'll likely either get it or you wont. But if you do then you're going to have one of the more powerful all around 3D applications as well as animation programs available. If you don't get it? don't worry, most don't. There are other mix of apps that will work just as well, just no real other all in one like it.
3rd Place - ZbrushCore (and Zbrush) - About the most powerful "clay" modeling app out there. Not free but only $150 for Core. Kinda finicky and far from an intuitive interface, but like Blender, if you can work past the interface issues, it will do some outrageous intense models only limited by your imagination.
Slightly off- Mudbox - from what I understand it's a close comp to Zbrush but better layout/interface .. But, wont run on my mac so who knows. 😖 . Worth a look at though.
