I haven't checked the new Outlook recently; maybe it's good. But all others that I know offer subpar service and honestly, look like crap. UX is important. For example, I cringe whenever someone makes me to use Roundcube-based webmail.
Yeah Roundcube's look definitely needs some help. Last year I did choose Roundcube for our webmail, but I spent several days altering its appearance so that it would look semi-professional.
I started with their new theme called "Larry" and then corrected the fonts, colors, graphics, and certain element sizing decisions.
