I use onshape because fusion360 is an autodesk product, and I avoid their
products if I can.
They have a bad track record, not from a “products don’t work” point of view,
but from a “use the courts to block people reselling their products” and
deliberatly breaking compatibility with competitor’s products.
Also, Fusion360 is only free if you are not a business, or are a small enough
business (based on your gross revenue, not profits).
Onshape is free as long as you make your designs free.
Both run in browsers, Onshape even runs on phones and tablets.
If you are not concered about issues other than “does it work”, either one will
work.