I have used both.
Schematics:
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Mentor: DX-Designer. Quite nice and reasonably complex editor.
I once had some problems with doubly assigned properties, but in general OK.
Cadence: (OrCAD) Capture; One of the worlds most spread schematic editors.
Can create netlists in a multitude of formats. Easy to get started with, but can also
do quite complex things.
Layout:
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Mentor: Very nice GUI, capable built-in parts library manager.
Messy to work with if designer and layout engineer is at different locations.
When I used it, it was far from stable. Had to manually fix designs.
It floods the layout folders with hundreds of files. There is even
a special menu tool that cleanes things up. Very nice padstack library manager.
Cadence: Inconsequent GUI (Try to set up Gerber files without tutorial...)
VERY powerful layout editor. You can do some really dangerous things
with it (handy if you are doing RF design). High learning threshold.
Because of being an old Unix design, using it is a bit akward but in the end
rewarding. Very nice and powerful constraint editor. Lacks good padstack
library editor. (Mentors' is superb!)
Pro: The layout is contained in ONE single file that is easily managed within a company.
Since I have worked as a consultant, I have come to appreciate Cadence OrCAD/PCB-Editor (Allegro)
because of the easy way it handles schematic files, netlists and layout databases. Variants
are very easily created.
I know of at least one company that uses DX-Designer (in netlist flow) for schematics and Allegro for layouts.
I myself have not explored that option.
I know that Cadence offers a "Lite" version for free, and I guess that Mentor most likely
must be willing to offer something similar. Mentor also has the PADS suite, but I am
not familiar at all with that tool.
My 5 cents...