I just played with Onshape for a little bit.

My overall impressions are good! The program completely redefines my thoughts for capabilities of DOM based applications and WebGL.

Pros:
Use anywhere on any device(Linux)! (DOM Based)
Free for personal use.
Scripting based design automation seems like first class citizens with the part monitoring and profiling features
Sheet metal capabilities are easy and intuitive. Something that I can't say for Solidworks.
You can straight up delete things in Onshape, Fusion 360 makes that a bit hard.
I like the fact that parts and assemblies are two explicitly different things.(Solidworks does this) It makes it easier for my brain to cut the "pie".
Fusion does it a more NX'y way where "a part is a part/assembly".
I don't have much experience with surfacing, so I can't comment about that aspect.
Git like branch/merge functionality with parts.

Cons:

It ain't the whole widget..
At the end of the day it's "just" a CAD program. Which is fine, but I feel that most consumers are getting "finer" tastes with the
advent of "the whole widget" design. Thanks Apple. (I don't mean that in a negative way either.) The thing that blew my mind about
Fusion 360, is that CAM is integrated and just works, CLOUD Based FEA/Rendering just works, FEA Analysis it's there, Topological
optimization there too. Rendering it's there also.

I see that on the apps developers on Onshape's store, are taking notice. Now you can download CAM add-on, render add-on, etc. I'm
scared that this is going the way of Solidworks/Jira/Confluence. Where you buy the base program. ($100 per month, then add CAM
/rendering/FEA separately). That $100 per month now looks like $200 per month. Now you are tied to vendor specific systems. Now you're
dependent on vendors for fixing their stuff when OnShape pushes an update. If the 3rd party vendor folds. Now all your legacy data is
effectively worthless. Or if there are problems, then 3rd party vendor blames Onshape, or Onshape blames vendor.

If Onshape makes the whole widget, then I have high confidence when an update is pushed, then CAM still works, render still works, and the UI is very
similar feeling. It makes me have trust that my "mechanical engineering workflow" just works.

When I use my mechanical engineering workflow. I want to be able to go from rough idea to CAD to FEA to render to 2d part drawings to CAM to "Part is
literally in my hand". With as little friction as possible. Adobe CC and Fusion 360 do this very well. I feel that with these industries where the data
model is incredibly complex. Own the whole pie is a requirement. Does that mean you need to lock-in your users? No. Give them escape hatches so they can use
familiar programs at whatever stage. Export as X, works well for this situation. But the main focus is making the UX/UI seamless between CAD/CAM/CAE. Fusion
360 in my opinion demolishes onShape in this regard.

Random side note. In the software engineering field, Companies that control the entire widget is "frowned upon". With good reason. The "data models" are
usually only text based (.C, .py, .js, .yaml,etc), and have open source standards associated with it. Meaning if you write Python in Visual Studio, the
same Python code will work in PyCharm. This is good. That means past the IDE stage, The files coming out are "clean and non-propriety", which allows you to
use any git-client you want. Git is open source and has a non-proprietary data model. So now you have the choice of using Github,Bitbucket,Gitlabs, etc. If
you don't like one, then switching is "painless".

Same goes for CI (Travis,Pipelines, etc,) To cloud providers (Kubernetes on Google Cloud, AWS, Azure etc). You're never locked in, since the data model at each stage is straightforward (text-based, that is interpreted to commonly agreed upon standards).

The CAD/CAM/CAE industry is nothing like this....which is why owning the whole widget, until/if common data models become prevalent.

OnShape's value proposition is a bit weak compared to Fusion 360.

Fusion 360 is free under ($100k of revenue per year), $300 a year for basic, and $1500 a year for Ultimate. (Basic will work for like 95% of users).

OnShape is free for personal/non-commercial use and everything needs to be publicly accessible. Then to go from personal to commerical/private. It's $1500 a year...just for CAD. Want the other features that Fusion 360 has? Open your wallet...

Fusion 360 in many respects, functions as a great drug dealer. They give you a little for free. They supply more value for you, as you need it. But the pricing is never so high , where you need to make hard call, and stop using their drugs. You grow with your drug dealer. Onshape is like "Here's enough for one hit", but if you want any more than that. Here's a brick, and I won't give it in little bags so you can give it to your friends at parties. You need to do it yourself....It's also a felony if you screw up when you try to buy in big.

Here's a good use case: I'm an at home inventor that wants to do a Kickstarter/Sharktank product. With OnShape, since it's commercial I need to front $1500 a year to solve only one piece of my product pie. Then more cash after that. With Fusion 360, I pay $0. If it takes off and I make over $100k. Paying $300 bucks a year is literally not a problem.

With this use case: OnShape isn't even on the radar for a CAD product to use.

But I always root for the underdog. But they have some work to do before they can have the same impact as Solidworks when came in out in the 90's. The DOM based app is really cool, and has alot of potential. But I don't plan on doing CAD on my Pixel2. The CAD/CAM/CAE workflow matters an order of magnitude more. Here's the cool thing. All of that can be computed in the DOM, so it can be developed down the line.

For year of 2015+ products, Fusion has the crown now.