[nuand]

Would anyone use Altium, KiCad, or Eagle if they had access to OrCAD, Allegro, or PADS?

Having used all of those tools, I can say that KiCad and Eagle will remain relegated to the low layer count, and at most moderately populated PCBs. Altium still has issues with large designs, but it's got its advantages, it's very easy to work with industrial designers within the Altium ecosystem. Altium also supports some decent auto-routing and DFM tools but does not have a simulator of any kind.

Cadence's OrCAD and Allegro offerings, and Mentor Graphic's PADS suite have tools for everything from designing with microvia (laser etched single layer vias) to highly configurable constraint management tools that allow for configuring some very powerful auto-routers and interactive tools. The big two tools also have simulators like PSICE, and integration with RF design tools like Keysight ADS, Genesys, Momentum, Hyperlynx, and HFSS. If your design has any RF components or high speed buses like DDR, PCIe and USB, you need to run your designs through these tools to verify your design. Eagle, and KiCAD are great for breakout boards. Altium can be used for some pretty simple products. But I'd never use anything but Cadence or Mentor Graphics tools for anything that had a signal that operated at more than 50MHz.

[blackguardx]

I think your Altium experience might be a little stale. Microvias in Altium are really easy since at least three or four years ago. It also supports basic SPICE simulation, but I've never used it. I use external SPICE and RF tools for most of my simulation needs. I've had good success designing RF boards in Altium and the only reason I would want to use Mentor Graphics would be if I had some massive digital design with high speed buses everywhere. You get what you pay for, but Altium is a solid tool at a decent price.

[reportingsjr]

KiCad also has support for microvias and blind/buried vias in this release. There are a few high speed design tools (trace length tuning and differential pair routing) that were added and I expect more RF support will come in the next release or two.