I recommend Debian, because it's easy to use and it's stable.
Arch is not stable, you'll lose a lot of time fixing stuff... Trust me I've been there, the package manager is shit and some times it overwrites files that should not be over written and that results in some programs not working or the OS not even booting up. You'll spend a lot of time fixing shit...
About customization:
If you want to customize how your system looks you should look into desktop environments and select the one you are the most comfortable in.
There are a shit load of desktop environments like Plasma, KDE, Gnome, Unit, etc.
The one I use is Gnome3, because it's easy to use and has loads of features, but you should look at some of them and select one that suits you.
Next you may want to look for themes and window managers for your desktop environment.
Just use google and you'll find something that looks cool. I don't use a theme myself so I can't recommend anything...
As for window managers there are a shit load of them also.
i3 is the one that is the most customizeble, there isn't anything you can't do in i3
OpenBox is more stable and it's extremely lightweight, it's easy to edit, but the default configuration is lacking basic features, when you start OpenBox for the first time, you'll see absolutely nothing.
Bottom line is, if you want something easy to setup and use, install Debian with Gnome, you don't need a theme and a WM to make it look sexy.
But if you want to make it look even sexier you can look into themes and WMs.
I hope you'll find this useful, good luck