I know a lot of people really like using xpvc. It is lighter than melamine and a lot stronger. I also find that the screws like to strip out of melamine.
i just finished building my first rack and i used a high end particle board. It was 20 dollars at home depot and they made all the cuts for me so all i had to do was drill it all together. The particle board i used looked really nice but did splinter several times. So if you use a high end particle board i would reccomend nailing rather than screwing. So to answer your question i would either use a high end particle board or 3/4 in plywood and then paint it