Debian will install X, desktop environment etc. for you if you want, so you can have a working environment straight away. Debian also has far more packages in the repositories. But if you do want to customise I found it simpler (not necessarily easier) to start from scratch the way you do in Arch, of course the same can be done with Debian by just installing core stuff. The biggest advantage of Arch in my opinion is that it is set up around a rolling release model, while Debian with Sid just doesn't feel quite right to me. Where you don't want a rolling release, like a server, Debian makes a lot more sense than Arch though.