The officials will likely reply here, too, but as a user, my opinion is that OneCNC is a top notch CADCAM that is able to automate much of the toolpathing work that you'd have to create manually in Bobcad.
OneCNC is able to correctly import 3d models put out by other programs. Bobcad is wireframe only.
Thus, OneCNC recognises and allows you to work with surfaces and solids.
OneCNC has a superior part rendering system, plus their backplot rendering will show you the actual toolpath scallops, should you desire to zoom in that close to see what the surface will look like.
I'm not knocking Bobcad (too hard ), but OneCNC has technical support that is capable of answering most any question, plus they seem to have programmers available that can actually attack program bugs. Bobcad has been very slow to patch their software, and many users are aggravated by that. If that's how they want to run their ship, I guess they are entitled to do it that way.
If I had known about OneCNC at the start (years ago when I bought my first seat of Bobcad), I likely would have been put off by the price. Bobcad fills a niche for an uncertain new user who just wants to tinker a bit, without spending a big chunk. But after a while, if your machining gets serious, you get tired of doing things the long way, and that is where Bobcad is weak.
So Bobcad will often get you by (if you have more time than money), but OneCNC will help you get some work done. I'm only sorry I don't get to program with OneCNC more than I do.
I do still have a use for Bobcad version 18, in that I use its scripting function to create some highly customised post processor scripts that alleviate the boring task of writing simple 2d type programs. In effect, my scripts are a poor man's attempt to simulate the superior "scripts" that OneCNC has incorporated in their software.
Both software companies have working demos. By all means try them out to see what suits you. The user interface is somewhat similar, so if you have experience in one program, some of what you are familiar with will carry across.