With Filament materials and sizes available in multiple sizes it gets confusing on choice of materials for a beginner. Here is easy to use guide on Filaments
1.75mm or 3mm?The general consensus says 3mm is easier to print with and 1.75mm gives better print quality, but there are a number of people who do amazing work with 3mm filament. My advice is start with 3mm and experiment with 1.75mm once you start pushing the limits there.One bit of advice if you do decide to try 1.75mm filament: Buy it on a spool. 1.75mm filament is a tangling nightmare if you do not buy it on a spool. I hate throwing those spools away, and tried a variety of DIY and even reusable commercial spools, but I was never able to get even remotely acceptable results. The extra costs and extra waste are annoying, but nothing compared to the hassles of unspooled 1.75mm filament.
via MendelMax.com Choosing Filament.
Another good writeup on Filaments and their use from RepRap Squad – Filaments and How They Work
From MatterHackers – 3D Printer Filament Comparison