Definitely Pages! You can't even make the font light or semibold or condensed in Word! It's just easier and completely different.[...]
Are you sure you are not accidentally mistaking different versions of the same typeface (e.g. Helvetica vs Helvetica Neue or the copy-cat Arial)?
Whether semibold, light etc is available or not is up to what is included in the actual font family, not the application in question. It's not magic. Those weights has to actually exist in the first place. Light and semibold weights aren't even designed in most cases (they're available in the Helvetica Neue family that comes with OS X iirc).
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When it comes to writing I'll never go back to word processors. Latex through and through. Try the
MacTex package if you're interested. The actual frontend or writing environment can be your favourite plain text/coding editor (if that's not an option there is one included in MacTex, called TexShop iirc). Plain-text is king.
If anyone reading has plans on trying it out make sure you go for xetex when compiling/typesetting, as it uses unicode and the fontspec package lets you use your existing ttf and otf fonts as-is.
Whether latex is a good writing environment is another issue. I'm fine with writing directly in markup but for longer passages I sometimes use something simple like
Byword,
iAWriter or
Multimarkdown Composer. Byword and Multimarkdown Composer both export to latex so that's pretty painless.
Should I ever need office-apps Libre Office is there to help out.
If Mellel ever reaches 3.0 I might check that out, though.